Part-stream distillation

ABSTRACT

A continuous process for preparing propylene oxide proceeds by (a) reacting propene with hydrogen peroxide in a reaction apparatus in the presence acetonitrile as solvent, obtaining a stream S0 containing propylene oxide, acetonitrile, water, at least one further component B; (b) separating propylene oxide from S0, obtaining stream S1 containing acetonitrile, water and B; (c) dividing S1 into streams S2 and S3; (d) subjects S3 to vapor-liquid fractionation in a first fractionation unit, obtaining vapor fraction stream S4a being depleted, relative to S3, of at least one of B and obtaining liquid bottoms stream S4b, and subjecting at least part of vapor fraction stream S4a to vapor-liquid fractionation in a second fractionation unit, obtaining vapor fraction stream S4c and liquid bottoms stream S4 being depleted, relative to S4a, of at least one of B; (e) recycling at least a portion of S4 to (a).

The present invention relates to a continuous process for thepreparation of propylene oxide wherein in a downstream acetonitrilesolvent recovery stage, a stream S1 containing the solvent acetonitrileand at least one component which has a normal boiling point which ishigher than the normal boiling point of acetonitrile, wherein thedecadic logarithm of the octanol-water partition coefficient (logK_(OW)) of the at least one component B, measured at 25° C., is greaterthan zero, is divided into two streams S2 and S3, wherein the totalweight of S3 relative to the total weight of S1 is in the range of from0.01 to 25%. The stream S3 is subjected to a vapor-liquid fractionationcomprising to serially coupled fractionation units, and a stream S4,obtained from the vapor-liquid fractionation and depleted of the atleast one component B, optionally after further work-up, is recycled assolvent stream to the epoxidation reaction.

Especially in industrial-scale continuous processes for the epoxidationof propene in acetonitrile as solvent, one of the key features of theoverall process is the recycling of the solvent back into theepoxidation step. An advantageous process which allows to effectivelyrecycle acetonitrile is described in WO 2011/006990 A1. This documentdiscloses a method for the separation of the acetonitrile from water,which method can be advantageously included in a continuous process forthe preparation of propylene oxide in acetonitrile as solvent. Carryingout this epoxidation process, it was found that although the processallows to achieve excellent results, in particular with regard to therecycling of acetonitrile, certain impurities, contained in in at leastone of the starting materials in the acetonitrile or in the hydrogenperoxide employed for the epoxidation reaction or obtained during theepoxidation reaction as by-products or side-products or formed during atleast one of the work-up stages which are preferably carried outdownstream the epoxidation reaction, may tend to a accumulate in theacetonitrile recycling stream. These impurities may further tend to havea negative influence on the performance of the heterogeneous catalystwhich is preferably employed in the epoxidation process, in particular azeolite-based catalyst having framework structure MWW and containing Ti.Such a decrease in performance may be observed either in a decrease inselectivity and/or in activity of the catalyst.

Therefore, it was an object of the present invention to provide aneconomically advantageous continuous process for the preparation ofpropylene oxide in acetonitrile as solvent which allows to essentiallyavoid the accumulation of such impurities in the recycling acetonitrilesolvent stream.

Usually, if such impurities accumulate in a certain stream, the streamis subjected to one or more suitable separation stages such asdistillation stages which, if carried out under suitable distillationconditions, may result in a stream depleted of the impurities. However,in particular in industrial-scale processes, subjecting a solventrecycling stream to such separation stages necessarily involvesconsiderable investment and energy consumption, due to the usually highflow rates and the thus resulting large apparatuses.

Surprisingly, however, it was found that for the separation ofimpurities from an acetonitrile recycling stream in a continuous processfor the preparation of propylene oxide, these disadvantage can beavoided by subjecting only a fraction of a specific recycling stream toimpurity separation using a specifically designed fractionation unit,and leaving the major portion of this specific recycling streamuntreated. For the impurities which were found to be critical, it wassurprisingly found that the performance of the catalyst can be ensuredover a very long period of time although only said minor fraction of arecycling stream is subjected to impurity separation.

Therefore, the present invention relates to a continuous process for thepreparation of propylene oxide, comprising

-   -   (a) reacting propene, optionally admixed with propane, with        hydrogen peroxide in a reaction apparatus in the presence of        acetonitrile as solvent, obtaining a stream S0 leaving the        reaction apparatus, S0 containing propylene oxide, acetonitrile,        water, at least one further component B, optionally propene and        optionally propane, wherein the normal boiling point of the at        least one component B is higher than the normal boiling point of        acetonitrile and wherein the decadic logarithm of the        octanol-water partition coefficient (log K_(OW)) of the at least        one component B is greater than zero;    -   (b) separating propylene oxide from S0, optionally after having        separated propene and optionally propane, obtaining a stream S1        containing acetonitrile, water and the at least one further        component B;    -   (c) dividing S1 into two streams S2 and S3, wherein the total        weight of S3 relative to the total weight of S1 is in the range        of from 0.01 to 25%;    -   (d) subjecting S3 to a vapor-liquid fractionation in a first        fractionation unit, obtaining a vapor fraction stream S4a being        depleted, relative to S3, of at least one of the at least one        component B and obtaining a liquid bottoms stream S4b, and        subjecting at least part of the vapor fraction stream S4a to a        vapor-liquid fractionation in a second fractionation unit,        obtaining a vapor fraction stream S4c and a liquid bottoms        stream S4 being depleted, relative to S4a, of at least one of        the at least one component B;    -   (e) recycling at least a portion of S4, optionally after        work-up, to (a), and recycling at least a portion of S2,        optionally after work-up, to (a).

Step (a)

According to step (a) of the present invention, propene, optionallyadmixed with propane, is reacted with hydrogen peroxide in a reactionapparatus in the presence of acetonitrile as solvent.

Generally, there are no specific restrictions how propene, optionallyadmixed with propane, is reacted with hydrogen peroxide, provided thatthe stream S0 is obtained leaving the reaction apparatus, which streamS0 contains propylene oxide, acetonitrile, water, the at least onefurther component B, and optionally propene and optionally propane.

Generally, it is conceivable to use a pure or essentially pure propeneas starting material and as stream subjected to the epoxidation in (a).Preferably, a mixture of propene and propene is used. If a mixture ofpropene and propane is used as stream subjected to the epoxidation in(a), the weight ratio of propene:propane is preferably at least 7:3. Forexample, commercially available propene can be employed which may beeither a polymer grade propene or a chemical grade propene. Typically,polymer grade propene has a propene content in the range of from 99 to99.8 weight-% and a propane content in the range of from 0.2 to 1weight-%. Chemical grade propene typically has a propene content in therange of from 92 to 98 weight-% and a propane content in the range offrom 2 to 8 weight-%. According to a preferred embodiment of the presentinvention, a mixture of propene and propane is subjected to theepoxidation which has a propene content in the range of from 99 to 99.8weight-% and a propane content in the range of from 0.2 to 1 weight-%.Therefore, the process of the present invention preferably comprises

-   -   (a) reacting propene, admixed with propane, with hydrogen        peroxide in a reaction apparatus in the presence of acetonitrile        as solvent, obtaining a stream S0 leaving the reaction        apparatus, S0 containing propylene oxide, acetonitrile, water,        at least one further component B, propane and optionally        propene, wherein the normal boiling point of the at least one        component B is higher than the normal boiling point of        acetonitrile and wherein the decadic logarithm of the        octanol-water partition coefficient (log K_(OW)) of the at least        one component B is greater than zero.

Preferably, the epoxidation reaction in (a) is carried out in thepresence of at least one suitable catalyst, preferably in the presenceof at least one suitable heterogeneous catalyst. Even more preferably,the at least one suitable catalyst comprises at least one zeolite which,in particular, contains Ti. Preferably, the at least one zeolitecontaining Ti has framework structure MWW. Even more preferably, thiszeolite containing Ti and having framework structure MWW, referred tohereinunder as TiMWW, contains at least one further heteroatom besidesTi. Among such further heteroatoms, Zn is most preferred. Such a zeolitecontaining Zn and Ti and having framework structure MWW is referred tohereinunder as ZnTiMWW.

The catalysts, especially preferably the titanium zeolite catalysts andstill more preferably TiMWW or ZnTiMWW, in particular ZnTiMWW, can beemployed as powder, as granules, as microspheres, as shaped bodieshaving, for example, the shape of pellets, cylinders, wheels, stars,spheres and so forth, or as extrudates such as extrudates having, forexample, a length of from 1 to 10, more preferably of from 1 to 7 andstill more preferably of from 1 to 5 mm, and a diameter of from 0.1 to5, more preferably of from 0.2 to 4 and especially preferably of from0.5 to 2 mm.

The preparation of such preferred TiMWW catalysts is described, e.g., inUS 2007043226 A1, in particular in Examples 3 and 5 of US 2007043226 A1.

As far as the preferred ZnTiMWW catalyst is concerned, it is still morepreferred to employ this catalyst in the form of a micropowder or in theform of a molding, wherein the molding preferably contains saidmicropowder.

Said ZnTiMWW catalyst in the form of a micropowder is preferablycharacterized by the following features and embodiments, including thecombinations of embodiments according to the given dependencies:

-   -   1. A micropowder, the particles of which having a Dv10 value of        at least 2 micrometer, said micropowder comprising mesopores        having an average pore diameter (4 V/A) in the range of from 2        to 50 nm as determined by Hg porosimetry according to DIN 66133,        and comprising, based on the weight of the micropowder, at least        95 weight-% of a microporous aluminum-free zeolitic material of        structure type MWW containing titanium and zinc (ZnTiMWW). The        Dv10 value is understood as being determined according to        Reference Example 2 of the present invention.    -   2. The micropowder of embodiment 1, having a Dv10 value in the        range of from 2 to 5.5 micrometer, preferably from 3 to 5.5        micrometer.    -   3. The micropowder of embodiment 1 or 2, having a Dv50 value in        the range of from 7 to 25 micrometer and a Dv90 value in the        range of from 26 to 85 micrometer. The Dv50 and Dv90 values are        understood as being determined according to Reference Example 2        of the present invention.    -   4. The micropowder of any of embodiments 1 to 3, wherein the        mesopores have an average pore diameter (4 V/A) in the range of        from 10 to 50 nm, preferably of from 15 to 40 nm, more        preferably of from 20 to 30 nm, as determined by Hg porosimetry        according to DIN 66133.    -   5. The micropowder of any of embodiments 1 to 4, additionally        comprising macropores having an average pore diameter (4 V/A) in        the range of from more than 50 nm, said macropores preferably        having an average pore diameter in the range of from 0.05 to 3        micrometer, as determined by Hg porosimetry according to DIN        66133.    -   6. The micropowder of any of embodiments 1 to 5, wherein the        micropores of the ZnTiMWW have an average pore diameter in the        range of from 1.10 to 1.16 nanometer as determined by nitrogen        adsorption according to DIN 66135.    -   7. The micropowder of any of embodiments 1 to 6, comprising,        based on the weight of the micropowder, at least 99 weight-%,        preferably at least 99.7 weight-% of the ZnTiMWW.    -   8. The micropowder of any of embodiments 1 to 7, wherein the        ZnTiMWW contains zinc in an amount of from 1.0 to 2.0 weight-%,        preferably of from 1.2 to 1.9 weight-%, more preferably of from        1.4 to 1.8 weight-%, calculated as Zn and based on the weight of        the ZnTiMWW.    -   9. The micropowder of any of embodiments 1 to 8, wherein the        ZnTiMWW contains titanium in an amount of from 1.0 to 2.0        weight-%, preferably of from 1.2 to 1.8 weight-%, more        preferably of from 1.4 to 1.6 weight-%, calculated as Ti and        based on the weight of the ZnTiMWW.    -   10. The micropowder of any of embodiments 1 to 9, having a        crystallinity, as determined by X-ray diffraction (XRD)        analysis, of at least 80%, preferably of at least 85%.    -   11. The micropowder of any of embodiments 1 to 10, comprising,        based on the total weight of the micropowder and calculated as        element, less than 0.001 weight-%, preferably less than 0.0001        weight-% of a noble metal, preferably selected from the group        consisting of gold, silver, platinum, palladium, iridium,        ruthenium, osmium, and a mixture of two or more thereof, more        preferably selected from the group consisting of gold, platinum,        gold, and a mixture of two or more thereof.    -   12. The micropowder of any of embodiments 1 to 11, comprising,        based on the total weight of the micropowder and calculated as        element, less than 0.1 weight.-%, preferably less than 0.01        weight-% of boron.    -   13. The micropowder of any of embodiments 1 to 12, having a bulk        density of in the range of from 80 to 100 g/ml.    -   14. The micropowder of any of embodiments 1 to 13, being a spray        powder, preferably obtainable or obtained by spray-drying.

Further, said ZnTiMWW catalyst in the form of a molding is preferablycharacterized by the following features and embodiments, including thecombinations of embodiments according to the given dependencies:

-   -   1. A molding, comprising a microporous aluminum-free zeolitic        material of structure type MWW containing titanium and zinc        (ZnTiMWW), said molding preferably comprising a micropowder        comprising, based on the weight of the micropowder, at least 95        weight-% of a microporous aluminum-free zeolitic material of        structure type MWW containing titanium and zinc (ZnTiMWW), said        molding more preferably comprising the micropowder according to        any of the micropowder embodiments 1 to 14 as described        hereinabove, the molding preferably further comprising at least        one binder, preferably a silica binder.    -   2. The molding of embodiment 1, comprising mesopores having an        average pore diameter in the range of from 4 to 40 nm,        preferably from 20 to 30 nm as determined by Hg porosimetry        according to DIN 66133.    -   3. The molding of embodiment 1 or 2, having a crystallinity, as        determined by XRD analysis, of at least 55%, preferably in the        range of from 55 to 75%.    -   4. The molding of any of embodiments 1 to 3, comprising the        micropowder in an amount in the range of from 70 to 80 weight-%        and the silica binder in an amount of from 30 to 20 weight-%,        the micropowder together with the silica binder constituting at        least 99 weight-% of the molding, wherein the molding has a        concentration of silanol groups with respect to the total number        of Si atoms of at most 6%, preferably at most 3%, as determined        according to ²⁹Si MAS NMR. The concentration of the silanol        groups is understood as being determined according to Reference        Example 3 of the present invention.    -   5. The molding of any of embodiments 1 to 4, being a strand        having circular cross-section and a diameter in the range of        from 1.5 to 1.7 mm and having a crush strength of at least 5 N,        preferably in the range of from 5 to 20 N, more preferably in        the range of from 12 to 20 N, the crush strength being        determined by crush strength test machine Z2.5/TS1S according to        the method as described in Reference Example 4 of the present        invention.    -   6. The molding of any of embodiments 1 to 5, the ²⁹Si-NMR        spectrum of said molding comprising six peaks at the following        position        -   peak 1 at −98+/−x ppm,        -   peak 2 at −104+/−x ppm,        -   peak 3 at −110+/−x ppm,        -   peak 4 at −113+/−x ppm,        -   peak 5 at −115+/−x ppm,        -   peak 6 at −118+/−x ppm,

with x in any of the peaks being 1.5, preferably 1.0, more preferably0.5,

wherein Q which is defined asQ=100*{[a ₁ +a ₂]/[a ₄ +a ₅ +a ₆]}/a ₃

is at most 1.6, preferably at most 1.4 and more preferably at most 1.3,with [a₁+a₂] being the sum of the peak areas of peaks 1 and 2, and[a₄+a₅+a₆] being the sum of the peak areas of peaks 4, 5, and 6, and a₃being the peak area of peak 3. These ²⁹Si-NMR characteristics areunderstood as being determined according the Reference Example 5 of thepresent invention.

-   -   7. The molding of any of embodiments 1 to 6, having a water        uptake in the range of from 3 to 8 weight-%, preferably from 4        to 7 weight-%, more preferably from 4.5 to 6.5 weight-%. The        water uptake is understood as being determined according to        Reference Example 6 of the present invention.    -   8. The molding of any of embodiments 1 to 7, the infrared        spectrum of said molding comprising a band in the region of 3746        cm⁻¹+/−20 cm⁻¹ and a band in the region of 3678 cm⁻¹+/−20 cm⁻¹,        wherein the intensity ratio of the band in the region of 3746        cm⁻¹+/−20 cm⁻¹ relative to the band in the region of 3678        cm⁻¹+/−20 cm⁻¹ is at most 1.5, preferably at most 1.4, more        preferably of at most 1.3, more preferably lower of at most 1.2.        These IR characteristics are understood as being determined        according the Reference Example 7 of the present invention.

A preferred process for the preparation of a preferred ZnTiMWW catalystand the respective characterization of this ZnTiMWW catalyst isdescribed in Reference Example 1 of the present invention.

Therefore, the present invention also relates to above-describedprocess, wherein in (a), propene is reacted with hydrogen peroxide inthe presence of a heterogeneous catalyst, said heterogeneous catalystpreferably comprising a zeolite, preferably a titanium zeolite, morepreferably a titanium zeolite of structure type MWW (TiMWW), morepreferably a zinc containing titanium zeolite of structure type MWW(ZnTiMWW).

Therefore, the process of the present invention preferably comprises

-   -   (a) reacting propene, admixed with propane, with hydrogen        peroxide in the presence of a heterogeneous catalyst, said        heterogeneous catalyst preferably comprising a zeolite,        preferably a titanium zeolite, more preferably a titanium        zeolite of structure type MWW (TiMWW), more preferably a zinc        containing titanium zeolite of structure type MWW (ZnTiMWW), in        a reaction apparatus in the presence of acetonitrile as solvent,        obtaining a stream S0 leaving the reaction apparatus, S0        containing propylene oxide, acetonitrile, water, at least one        further component B, propane and optionally propene, wherein the        normal boiling point of the at least one component B is higher        than the normal boiling point of acetonitrile and wherein the        decadic logarithm of the octanol-water partition coefficient        (log K_(OW)) of the at least one component B is greater than        zero.

Generally, the reaction in (a) can be carried out in any appropriateway. Thus, for example, it can be carried out in a batch reactor or inat least one semi-continuously operated reactor or in at least onecontinuously operated reactor. The continuous mode of operation ispreferred, wherein the reaction is preferably carried out at atemperature in the range of from −10 to 120° C., more preferably from 30to 90° C., more preferably from 30 to 65° C. Preferably, the temperatureat which the reaction is carried out is not kept constant during thereaction but is adjusted continuously or step-wise to allow for aconstant hydrogen peroxide conversion as determined in stream S0 leavingthe reactor in which the epoxidation reaction in (a) is carried out.Preferably, the reaction in (a) is carried out in at least onecontinuously operated reactor such as a tube reactor or a tube bundlereactor which preferably contains at least one cooling jacketsurrounding the at least one tube. If the reaction in (a) is carried outin such a reactor containing at least one cooling jacket, the term“reaction temperature” as used herein refers to the temperature of thecooling medium when entering the cooling jacket. Generally, due tocatalyst deactivation, the reaction temperature is continuously orstep-wise increased. Preferably, the reaction temperature iscontinuously or step-wise increased by 1° C./d at most, more preferablyby less than 1° C./d. Preferably, the hydrogen peroxide conversion whichis preferably kept constant is at least 80%, more preferably at least85%, more preferably at least 90%, more preferably in the range of from90 to 95%. The principle of a preferred hydrogen peroxide conversiondetermination is described in Example 1, section 1.1 a) hereinbelow. Thepressures in the at least one reactor are generally in the range from 3to 100 bar, preferably from 15 to 45 bar. In particularly preferredembodiments of the process of the present invention, the reaction iscarried out at temperatures and pressures at which the reaction mixtureis liquid and no gas phase is present in the at least one reactorwherein two or more liquid phases may exist. The molar ratio of propenerelative to hydrogen peroxide with regard to the starting materialspassed into the at least one reactor in which epoxidation is carried in(a) is preferably in the range of from 0.9:1 to 3.0:1, more preferablyfrom 0.98:1 to 1.6:1, more preferably from 1.0:1 to 1.5:1. The amount ofacetonitrile passed to the at least one reactor is adjusted so that thehydrogen peroxide concentration of the overall stream passed to the atleast one reactor in which the epoxidation is carried out in (a) ispreferably in the range of from 2 to 20 weight-%, more preferably from 5to 12 weight-%, based on the total weight of the overall stream.

Preferably, the overall stream passed to the at least one epoxidationreactor, i.e. the reactor feed, contains of from 50 to 80 weight-%, morepreferably from 60 to 70 weight-% acetonitrile, of from 7 to 14weight-%, more preferably from 8 to 11 weight-% propene, of from 5 to 12weight-%, more preferably from 6 to 10 weight-% hydrogen peroxide, andof from 10 to 25 weight-%, preferably from 12 to 20 weight-% water.

Preferably, the reaction in (a) is carried out in two or more stages,preferably in two or three stages, more preferably in two stages.Preferably, a two-stage reaction comprises:

-   -   (a1) reacting propene, optionally admixed with propane, with        hydrogen peroxide, preferably in the presence of a heterogeneous        catalyst, said heterogeneous catalyst preferably comprising a        zeolite, preferably a titanium zeolite, more preferably a        titanium zeolite of structure type MWW (TiMWW), more preferably        a zinc containing titanium zeolite of structure type MWW        (ZnTiMWW), in a reaction apparatus in the presence of        acetonitrile as solvent, obtaining a stream S0-a1 leaving the        reaction apparatus, S0-a1 containing propylene oxide,        acetonitrile, water, optionally at least one further component        B, optionally propane, optionally propene, and unreacted        hydrogen peroxide;    -   (a2) separating propylene oxide from S0-a1, obtaining a stream        S0-a2-1 being enriched in propylene oxide and depleted of        hydrogen peroxide, and a stream S0-a2-2 being depleted of        propylene oxide and comprising unreacted hydrogen peroxide,        acetonitrile, and water;    -   (a3) subjecting the stream S0-a2-2, preferably after admixing        with propene optionally admixed with propane, to epoxidation        reaction conditions, preferably in the presence of a        heterogeneous catalyst, said heterogeneous catalyst preferably        comprising a zeolite, preferably a titanium zeolite, more        preferably a titanium zeolite of structure type MWW (TiMWW),        more preferably a zinc containing titanium zeolite of structure        type MWW (ZnTiMWW), in a reaction apparatus obtaining a stream        S0-a3 leaving the reaction apparatus, S0-a3 containing propylene        oxide, acetonitrile, water, optionally at least one further        component B, optionally propane, and optionally propene;

wherein either S0-a1 and/or S0-a3 contain at least one further componentB and wherein the normal boiling point of the at least one component Bis higher than the normal boiling point of acetonitrile and wherein thedecadic logarithm of the octanol-water partition coefficient (logK_(OW)) of the at least one component B is greater than zero.

In a preferred set-up of the process of the present invention as shownin FIG. 1 hereinbelow, the stream (5) is a preferred stream S0-a1, thestream (6) is a preferred stream S0-a2-1, the stream (7) is a preferredstream S0-a2-2, and the stream (9) is a preferred stream S0-a3. Thestream (8) in FIG. 1 is a preferred stream of propene optionally admixedwith propane which is preferably admixed in (a3).

Preferably, the streams S0-a2-1 and S0-a3 together constitute the streamS0 according to the present invention.

As far as the preferred epoxidation reaction conditions of stage (a1)are concerned, reference is made to the preferred epoxidation reactionas discussed above. The hydrogen peroxide can be separated off accordingto (a2) by any suitable methods. The hydrogen peroxide is preferablyseparated off by distillation using one or more distillation towers,preferably one distillation tower. This distillation tower is preferablyoperated at conditions allowing for obtaining a top stream whichcontains hydrogen peroxide in an amount of at most 100 weight-ppm, basedon the total weight of the top stream, preferably containing essentiallyno hydrogen peroxide.

Additionally this distillation tower is preferably operated atconditions allowing for obtaining a top stream which contains at least80%, more preferably at least 90% more preferably at least 95% of thepropylene oxide contained in the feed stream S0-a1. Preferably, thisdistillation tower has of from 15 to 45, preferably from 20 to 40theoretical trays and is operated at a pressure at the top of the towerin a range of from 0.5 to 1.2 bar, preferably from 0.7 to 1.1 bar. Thereflux ratio of this distillation tower is preferably in the range offrom 0.05:1 to 0.5:1, more preferably from 0.1:1 to 0.2:1. The bottomsstream obtained from the distillation tower in (a2), containingessentially all of the unreacted hydrogen peroxide from (a1) and furthercontaining acetonitrile, water, is preferably passed to stage (a3). Asfar as stage (a3) is concerned, it is preferred to use an adiabaticreactor, preferably an adiabatic shaft reactor. The epoxidationconditions in (a3) are preferably chosen to allow for a hydrogenperoxide conversion at the outlet of (a3) of at least 99%, preferably atleast 99.5%, more preferably at least 99.9% based on the hydrogenperoxide fed to (a1). In (a3), it is preferred to use the same catalystas in (a1). As far as the propene is concerned which is preferablyintroduced into the reactor used in (a3), reference is made to thepropene already discussed hereinabove in the context of (a). Thus, forexample, chemical grade propene or polymer grade propene can be used,with polymer grade propene being preferred. If stages (a1) and (a3) areperformed, the reactors are preferably operated so that the overallpropene conversion, taking into account conversion in (a1) andconversion in (a3), is at least 65%, more preferably at least 70%, morepreferably at least 75%.

Depending on the specific epoxidation conditions in (a), S0 may containany conceivable amounts of propylene oxide, acetonitrile, water, the atleast one further component B, optionally propene and optionallypropane. Preferably, from 90 to 97 weight-%, more preferably from 92 to97 weight-%, more preferably from 95 to 97 weight-% of S0 consist ofacetonitrile, water, and propylene oxide, and from 0.01 to 3 weight-%,more preferably from 0.015 to 2 weight-%, more preferably from 0.02 to0.1 weight-ppm of S0 consist of the at least one component B. The term “. . . weight-% of S0 consist of the at least one component B” refers tothe overall amount of all components B contained in S0. More preferably,from 90 to 97 weight-%, more preferably from 92 to 97 weight-%, morepreferably from 95 to 97 weight-% of S0 consist of acetonitrile, water,and propylene oxide, from 0.05 to 7 weight-%, more preferably from 0.1to 6 weight-%, more preferably from 0.15 to 4 weight-% consist ofpropene and optionally propane, and wherein from 0.01 to 3 weight-%,preferably from 0.015 to 2 weight-%, more preferably from 0.02 to 1weight-ppm of S0 consist of the at least one component B.

According to the present invention, the decadic logarithm of theoctanol-water partition coefficient (log K_(OW)) of the at least onecomponent B is greater than zero. The octanol-water partitioncoefficient (log K_(OW)) is a parameter well-known by the skilledperson. For the sake of completeness, its definition and itsdetermination are described in Reference Example 8 hereinbelow.

Typically, the at least one component B contained in S0 either is aby-product and/or a side-product obtained during the epoxidationreaction in (a), and/or is a compound which is formed during at leastone of the work-up stages being preferably carried out downstream of (a)and which accumulates if certain process streams of the preferredintegrated process are recycled into (a), and/or is contained as animpurity in at least one of the starting materials employed in (a) suchas an impurity in the acetonitrile or an impurity in the hydrogenperoxide.

Preferably, the at least one component B is propionitrile,1-nitropropane, 2-nitropropane, 3-methylbutanenitrile, n-pentanenitrile,1-pentanol, 2-pentanol, 2-butanone, 2-pentanone, 2-hexanone,4-methyl-2-heptanone, 2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, 4,6-dimethyl-2-heptanone,2,6-dimethyl-4,6-heptandiol, 2,4-dimethyl-oxazoline,2,5-dimethyloxazoline, cis-2,4-dimethyl-1,3-dioxolane,trans-2,4-dimethyl-1,3-dioxolane, acetaldehyde, propionaldehyde,2-butanone at least one impurity contained in the hydrogen peroxideemployed in (a), or a combination of two or more of these compounds.

Preferably, the at least one component B includes propionitrile,1-nitropropane, 2-nitropropane, 2,6-dimethyl-4-heptanol,4,6-dimethyl-2-heptanol, 2,6-dimethyl-4-heptanone, acetaldehyde,propionaldehyde, 2-butanone, or a combination of two or more of thesecompounds. More preferably, the at least one component B includes acombination of three or more of these compounds, more preferably acombination of four or more of these compounds, more preferably acombination of five or more of these compounds. More preferably, the atleast one component B includes a combination of propionitrile,1-nitropropane, 2-nitropropane, 2,6-dimethyl-4-heptanol,4,6-dimethyl-2-heptanol, and 2,6-dimethyl-4-heptanone. Also preferably,the at least one component B includes a combination of seven or more ofthese compounds, more preferably a combination of eight or more of thesecompounds. More preferably, the at least one component B includes acombination of propionitrile, 1-nitropropane, 2-nitropropane,2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, acetaldehyde, and propionaldehyde. Alsopreferably, the at least one component B includes a combination of nineor more of these compounds. More preferably, the at least one componentB includes a combination of propionitrile, 1-nitropropane,2-nitropropane, 2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, acetaldehyde, propionaldehyde, and 2-butanone.

Regarding the at least one impurity contained in the hydrogen peroxideemployed in (a), this at least one impurity is preferably an alkylphosphate such as tris-(2-ethylhexyl) phosphate, a nonyl alcohol such asdiisobutylcarbinol, an alkylcyclohexanol ester such as2-methyl-cyclohexylacetate, an N,N-dialkyl carbonamide such asN,N-dibutylpropionamide, an N-alkyl-N-aryl carbonamide such asN-ethyl-N-phenylbenzamide, an N,N-dialkyl carbamate such as2-ethylhexyl-N-butylcarbamate, a tetraalkyl urea such astetra-n-butylurea, a cycloalkyl urea such as dihexyl propeneurea, aphenylalkyl urea such as N,N-dibutyl-N′-methyl-N′-phenylurea, anN-alkyl-2-pyrrolidone such as octyl pyrrolidone, an N-alkyl caprolactamsuch as n-octyl caprolactam, C₈-C₁₂ alkyl aromatic compounds, dibutylamine, dibutyl formamide, 1-butanol, butyric aldehyde, 2-ethylhexanol,2-ethylanthraquinone, 2-ethyl-5,6,7,8-tetrahydroanthra-quinone, or acombination of two or more of these compounds.

It is conceivable that the reacting propene, admixed with propane, withhydrogen peroxide in the presence of a heterogeneous catalyst, saidheterogeneous catalyst preferably comprising a zeolite, preferably atitanium zeolite, more preferably a titanium zeolite of structure typeMWW (TiMWW), more preferably a zinc containing titanium zeolite ofstructure type MWW (ZnTiMWW), in a reaction apparatus in the presence ofacetonitrile as solvent, such as reacting propene in (a1) and/or (a3),is carried out in the presence of at least one potassium salt which isdissolved in the respective mixtures which are subjected to epoxidationconditions in (a), such as in (a1) and/or (a3). Preferably, the at leastone potassium salt is selected from the group consisting of at least oneinorganic potassium salt, at least one organic potassium salt, andcombinations of at least one inorganic potassium salt and at least oneorganic potassium salt, wherein preferably at least one of the at leastone potassium salt is an organic potassium salt. More preferably, the atleast one potassium salt is selected from the group consisting of atleast one inorganic potassium salt selected from the group consisting ofpotassium hydroxide, potassium halides, potassium nitrate, potassiumsulfate, potassium hydrogen sulfate, potassium perchlorate, dipotassiumhydrogen phosphate, potassium dihydrogen phosphate, at least one organicpotassium salt selected from the group consisting of potassium salts ofaliphatic saturated monocarboxylic acids preferably having 1, 2, 3, 4, 5or 6 carbon atoms, potassium carbonate, and potassium hydrogencarbonate, and a combination of at least one of the at least oneinorganic potassium salts and at least one of the at least one organicpotassium salts. More preferably, the at least one potassium salt isselected from the group consisting of at least one inorganic potassiumsalt selected from the group consisting of potassium hydroxide,potassium chloride, potassium nitrate, at least one organic potassiumsalt selected from the group consisting of potassium formate, potassiumacetate, potassium carbonate, and potassium hydrogen carbonate, and acombination of at least one of the at least one inorganic potassiumsalts and at least one of the at least one organic potassium salts.

Therefore, the present invention also relates to a process wherein (a)comprises reacting propene, optionally admixed with propane, withhydrogen peroxide in a reaction apparatus in the presence ofacetonitrile as solvent and in the presence of at least one dissolvedpotassium salt, obtaining a stream S0 leaving the reaction apparatus, S0containing propylene oxide, acetonitrile, water, at least one furthercomponent B, optionally propene and optionally propane, wherein thenormal boiling point of the at least one component B is higher than thenormal boiling point of acetonitrile and wherein the decadic logarithmof the octanol-water partition coefficient (log K_(OW)) of the at leastone component B is greater than zero.

Step (b)

According to step (b) of the process of the present invention, propyleneoxide is separated from S0, and a stream S1 is obtained which, comparedto S0, is depleted of propylene oxide and which contains acetonitrile,water and the at least one further component B. If S0 additionallycontains propene and/or propane, it is preferred that the propene and/orthe propane are also separated from S0 to obtain a stream S1 is obtainedwhich, compared to S0, is depleted of propylene oxide, propene and/orpropane, and which contains acetonitrile, water and the at least onefurther component B. Further, if S0 additionally contains oxygen, it ispreferred that the oxygen is also separated from S0 a stream S1 isobtained which, compared to S0, is depleted of propylene oxide andoxygen and which contains acetonitrile, water and the at least onefurther component B. Preferably, S0 obtained according to the process ofthe present invention contains propene, propane, and optionally oxygen,and apart from propylene oxide, propene, propane and optionally oxygenare separated from S0 to obtain S1 which, compared to S0, is depleted ofpropylene oxide, propene and propane and optionally oxygen, and whichcontains acetonitrile, water and the at least one further component B.

Regarding the separation of the propene and/or the propane, and/or theoxygen from S0, no specific restrictions exist. In particular, allconceivable sequences of separation of the individual components and allconceivable separation techniques such as distillation are possible.Therefore, it is conceivable to separate the propene and/or the propaneand optionally the oxygen together with propylene oxide from S0 toobtain S1. The separated stream enriched in propene and/or propane andoptionally oxygen is then preferably subjected to suitable separationstages and/or work-up stages from which a stream is obtained whichessentially consists of propylene oxide as valuable product. Preferably,the stream S0 is subjected to a first separation stage where propene andoptionally propane are separated. If S0 additionally contains oxygen, itis preferred that the oxygen is separated together with the propeneand/or the propane.

Therefore, the present invention relates to the process as describedabove, comprising (b) separating propylene oxide from S0, after havingseparated propene and optionally propane, obtaining a stream S1containing acetonitrile, water and the at least one further component B.Also, the present invention relates to the process as described above,comprising (b) separating propylene oxide from S0, after havingseparated propene and propane, obtaining a stream S1 containingacetonitrile, water and the at least one further component B. Also, thepresent invention relates to the process as described above, comprising(b) separating propylene oxide from S0, after having separated propene,propane, and optionally oxygen, obtaining a stream S1 containingacetonitrile, water and the at least one further component B. Also, thepresent invention relates to the process as described above, comprising(b) separating propylene oxide from S0, after having separated propene,propane, and oxygen, obtaining a stream S1 containing acetonitrile,water and the at least one further component B.

Therefore, it is preferred that step (b) of the process of the presentinvention comprises a step (I) wherein propene, optionally together withpropane, and oxygen which is optionally additionally contained in S0,are separated from S0 to obtain a stream S01 enriched in propyleneoxide, acetonitrile, water, and the at least one component B whichstream S01 is depleted of propene, optionally propane, and oxygen; andfurther comprises a step (II) wherein propylene oxide is separated fromS01, obtaining a stream S02 enriched in acetonitrile, water and the atleast one component B which stream S02 is depleted of propylene oxide.

Regarding to separation in (I), no specific restrictions exist.Preferably, the separation is carried out so that at least 90 weight-%,more preferably at least 95 weight-%, more preferably at least 98weight-%, more preferably at least 99 weight-% of S01 consist ofacetonitrile, water, the at least one component B and propylene oxide.Preferably, a fractionation unit is employed for the separation in (I).Further preferably, the separation in (I) is carried out in at least onedistillation tower, more preferably in one distillation tower. From thisdistillation tower, S01 is preferably obtained as bottoms stream.Preferably, this distillation tower has from 10 to 30, more preferablyfrom 15 to 25 theoretical trays. The distillation tower is preferablyoperated at a top pressure of from 0.5 to 1.2 bar, more preferably offrom 0.7 to 1.1 bar. In order to facilitate said separation task, it wasfound that it is advantageous to add either liquid acetonitrile or aliquid mixture of acetonitrile with water to the top of the column. Itis believed that this external reflux serves as entraining agent which,among others, prevents propylene oxide from being separated via the topof the distillation tower. According to a preferred embodiment of thepresent invention, a portion of the bottom stream of the distillationtower preferably employed in stage (II) is used. It is also conceivablethat the stream TL2 described hereinbelow or a portion thereof is usedas entraining agent. The amount of TL2 will not be sufficient, andanother stream is to be added. Preferably, the weight ratio of theamount of acetonitrile fed as external reflux to the top of thedistillation tower relative to the weight of the stream S0 fed into thedistillation tower and to be separated in the distillation tower is inthe range of from 1:1 to 4:1 preferably from 1.5:1 to 3:1. Thetemperature of the external reflux is generally in the range of from 2to 20° C., preferably in the range of from 5 to 15° C. According to thepresent invention, preferably at least 85 volume-%, more preferably atleast 90 volume-%, more preferably at least 93 volume-% of the topstream of the distillation column according to (I) consist of propene,oxygen, and optionally propane. Depending on its oxygen content, thistop stream can be passed to a further suitable workup stage wherein theoxygen content is suitably decreased in order to allow, e.g., forrecycling the oxygen-depleted stream to be recycled to one or morestages of the present invention, such as a starting material for stage(a) of the inventive process like stage (a1) or stage (a3), or asportion of the stream P described hereinbelow. If the oxygen content ofsaid top stream is reduced, it is preferred to reduce the oxygen byreaction with hydrogen in the presence of a suitable catalyst. Suchcatalysts are, for example, catalysts comprising tin and at least onenoble metal as described in WO 2007/000396 A1, in particular in Example1 of WO 2007/000396 A1. It is also conceivable to use catalystscomprising copper in elemental and/or oxidic form on a support, whereincopper is present on the support in an amount of 30 to 80 weight-% basedon the whole catalyst and calculated as CuO. Such catalysts can beprepared, for example, according to the example of EP 0 427 062 A2,catalyst 2, page 4, lines 41 to 50 (corresponding to U.S. Pat. No.5,194,675). In order to reduce the oxygen content, also other suitablemethods are conceivable. Optionally, said top stream, prior to besubjected to hydrogenation, can be compressed and partially condensedwherein a liquid stream is obtained which essentially consists ofpropene and optionally propane and acetonitrile and which contains minoramounts of water. The non-condensed portion essentially consists ofpropene and optionally propane and oxygen and contains a minor amount ofwater wherein, compared to the basic stream, the oxygen content isincreased while still being in a range so that the mixture is notignitable. This oxygen-enriched stream is then subjected tohydrogenation.

As mentioned above, prior to using the stream S01 as stream S1 accordingto the present invention, it is especially preferred to separatepropylene oxide from S01 in (II) to obtain a stream S02 which isessentially free of propylene oxide. Regarding to separation in (II), nospecific restrictions exist. Preferably, the separation is carried outso that preferably at least 90 weight-%, more preferably at least 95weight-%, more preferably at least 99 weight-% of S02 consist ofacetonitrile, water and the at least one component B. More preferably,the weight ratio of acetonitrile relative to water in S02 is greaterthan 1:1, preferably in the range of from 2:1 to 10:1, more preferablyfrom 2.5:1 to 5:1. Preferably, a fractionation unit is employed for theseparation in (II). Further preferably, the separation in (II) iscarried out in at least one distillation tower, more preferably in onedistillation tower. Preferably, this tower has of from 50 to 80, morepreferably of from 60 to 70 theoretical trays. The distillation tower ispreferably operated at a top pressure of from 0.2 to 2 bar, morepreferably of from 0.4 to 1 bar. Optionally, at least one suitable polarsolvent or a mixture of two or more polar solvents, preferably water,can be added in the upper part of the column as extractive agent.According to an embodiment of the process of the present invention, theseparation according to stage (III) can be carried out by

-   -   introducing S01 into an extractive distillation column;    -   additionally introducing a polar extracting solvent or a mixture        of two or more thereof, preferably water, into said extractive        distillation column;    -   distilling propylene oxide overhead from said extractive        distillation column as top stream, wherein the top stream        comprises only minor amounts of acetonitrile such as 500 ppm or        less;    -   compressing said top stream obtained overhead in the previous        step by means of at least one compressor to give a compressed        vapor;    -   condensing the compressed vapor obtained in the previous step        and returning at least part of the heat of condensation to at        least one reboiler employed in the extractive distillation        column.

From this distillation tower according to (II), a top stream is obtainedwhich contains at least 90 weight-%, preferably at least 95 weight-%,more preferably at least 99 weight-% of propylene oxide. Further fromthis distillation tower, S02 is preferably obtained as bottoms streamwhich preferably contains 500 weight-ppm at most, preferably 100weight-ppm at most, and more preferably 60 weight-ppm at most ofpropylene oxide, based on the weight of S02.

Depending on the requirements on the propylene oxide quality, it isconceivable to use this propylene oxide fraction without any furtherpurification. It is, however, also conceivable to further purify saidpropylene oxide fraction, for example in at least one furtherdistillation stage.

From the distillation tower according to (II) or optionally from thefurther distillation stage, a propylene oxide stream is obtained whereinat least 99.5 weight-%, more preferably at least 99.9 weight-%, morepreferably at least 99.999 weight-% of said stream consist of propyleneoxide. Therefore, the present invention also relates to a compositioncomprising at least 99.999 weight-% of propylene oxide, obtainable orobtained by a process as described above and comprising the separationstage (II).

Thus, the present invention preferably relates to the process asdescribed above, wherein (b) comprises

-   -   (I) separating propene, optionally together with propane, and        oxygen which is optionally additionally contained in S0, from        S0, obtaining a stream S01 enriched in propylene oxide,        acetonitrile, water, and the at least one component B, wherein        preferably at least 99 weight-% of S01 consist of acetonitrile,        water, the at least one component B and propylene oxide; wherein        for separation, preferably a fractionation unit is used, wherein        preferably, at the top of the fractionation unit, liquid        acetonitrile, optionally admixed with liquid water, is added as        entraining agent;    -   (II) separating propylene oxide from S01, obtaining a stream S02        enriched in acetonitrile, water and the at least one component        B, wherein preferably at least 95 weight-% of S02 consist of        acetonitrile, water and the at least one component B, and        wherein the weight ratio of acetonitrile relative to water is        greater than 1:1.

Preferably, S02 obtained from step (b), preferably from step (II)comprised in (a), is subjected to step (c) as stream S1.

Preferably, from 90 to 99.9 weight-%, more preferably from 95 to 99.8weight-%, more preferably from 99 to 99.7 weight-% of S1 consist ofacetonitrile and water, and preferably from 0.01 to 5 weight-%, morepreferably from 0.015 to 3 weight-%, more preferably from 0.02 to 2weight-% of S1 consist of the at least one component B.

Optionally, at least a portion of S02 is diverted and used as entrainingagent in the fractionation unit according to (I) as described above.Preferably, if used as entraining agent, from 15 to 35%, more preferablyfrom 20 to 35% of S02 are diverted and preferably added at the top ofthe fractionation unit used in (I).

Optional Additional Step(s) Comprised in (b)

Depending on the specific conditions during the upstream stages of theprocess of the present invention, namely stages (a), (I) and (II), thebottoms stream obtained from the distillation tower according to (II)may also contain certain amounts of hydroperoxides such as certainamounts of hydrogen peroxide and/or certain amounts of organichydroperoxides, for example, 1-hydroperoxypropanol-2 and/or2-hydroperoxypropanol-1. Preferably, the bottoms stream obtained fromthe distillation tower according to (III) may contain at most 2weight-%, more preferably at most 1 weight-% of these hydroperoxides intotal, based on the weight of the bottoms stream. In order to reduce thehydroperoxide content and, thus, to avoid the build-up of thehydroperoxides which are believed to possibly have a detrimentalinfluence as far as the formation of undesirable by-products and safetyaspects based on the decomposition of the hydroperoxides are concerned,it is conceivable to subject said bottoms stream obtained from thedistillation tower according to (II) to at least one further processstage. Said build-up especially occurs if the inventive highlyintegrated process is realized. While every suitable method for at leastpartially removing these hydroperoxides is conceivable, it is especiallypreferred to catalytically reduce, preferably to catalyticallyhydrogenate the hydroperoxides. As suitably catalyst, a catalyst may bementioned which is described in US 2004068128 A1, in particular inparagraphs [0053] to [0076]. Preferred catalysts are selected from thegroup consisting of heterogeneous catalysts comprising Ru, Ni, Pd, Pt,either individually or as a mixture of two or more thereof, as activemetal on a suitable support material. An especially suitable catalyst,namely a supported catalyst comprising 5 weight-% of Pd on activatedcarbon is, described in Example E2 of US 2004068128 A1. The pressureduring hydrogenation is typically in the range of from 1 to 100bar(abs), preferably from 1 to 10 bar(abs), and the temperature duringhydrogenation is typically in the range of from 0 to 180° C., preferablyfrom 25 to 120° C., more preferably from 65 to 85° C. The hydrogenpartial pressure during hydrogenation is preferably in the range of frommore than 1 to 20 bar, more preferably from 2 to 15 bar, more preferablyfrom 3 to 13 bar. If the hydrogenation is carried out in a fixed bed,which is preferred, the residence time of the liquid passed through thehydrogenation reactor is generally in the range of from 1 second (s) to1 hour (h), preferably from 10 s to 20 minutes (min), in particular from30 s to 5 min. Depending on the reaction conditions employed forreducing, preferably hydrogenating the bottoms stream obtained from thedistillation tower according to (II), it may be necessary to separatethe resulting stream from the catalyst, preferably hydrogenationcatalyst and/or non-reacted reducing agent, preferably hydrogen and/orby-products from the hydrogenation, preferably CO and/or methane. Inparticular, the stream resulting from reduction, preferablyhydrogenation, contains at least 95 weight-% acetonitrile and water,based on the total weight of the bottoms stream, wherein the weightratio of acetonitrile relative to water is preferably greater than 1:1.Generally, it is conceivable to use this stream obtained from thehydrogenation and preferably separation of the catalyst as stream S1 ofthe present invention.

Depending on the specific conditions during the upstream stages of thepresent invention, i.e. stages (a), (I) and (II), and the reduction,preferably the hydrogenation stage, the stream obtained from reduction,preferably hydrogenation may contain certain amounts of acetaldehyde andoptionally further low boilers such as, for example, propionaldehyde andacetone. Typically, this stream may contain up to 2000 weight-ppm,preferably up to 1000 weight-ppm, more preferably up to 300 weight-ppmof acetaldehyde and other low-boilers in total, based on the totalweight of this stream. In order to reduce the acetaldehyde content andoptionally the content with respect to the other low boilers and, thus,to avoid the build-up of these compounds which especially occurs if theinventive highly integrated process is realized, it is preferred tosubject this stream to at least one further process stage. While everysuitable method for at least partially removing acetaldehyde isconceivable, it is especially preferred to separate acetaldehyde atleast partially from the stream by distillation. Separation according tothis stage is preferably carried out in at least one distillation tower,more preferably in one distillation tower. Preferably, this tower has offrom 15 to 40, more preferably of from 20 to 35 theoretical trays. Thedistillation tower is preferably operated at a top pressure in the rangeof from 0.7 to 2 bar, more preferably from 1.1 to 2 bar.

From this distillation tower, a bottoms stream is obtained whichpreferably contains 200 weight-ppm at most, preferably 100 weight-ppm atmost, more preferably 50 weight-ppm at most of acetaldehyde and otherlow boilers in total, based on the weight of the bottoms stream.Preferably, at least 98 weight-%, more preferably at least 98.5weight-%, more preferably at least 98.7 weight-% of the bottoms streamconsist of acetonitrile, water, and the at least one component B.Preferably, at least 98 weight-%, more preferably at least 98.5weight-%, more preferably at least 98.7 weight-% of the bottoms streamconsist of acetonitrile, water and the at least one component B, andwherein the weight ratio of acetonitrile relative to water is greaterthan 1:1. Generally, it is conceivable to use this bottoms stream asstream S1 in the process of the present invention. According to aconceivable embodiment of the present invention, no such distillationstage is performed.

Therefore, the present invention also relates to the process asdescribed above, wherein (b) further comprises

(IIIa) subjecting S02 obtained from (II) to hydrogenation; and/or

(IIIb) subjecting the stream obtained from (II) or (IIIa) todistillation to obtain a bottoms stream, wherein the hydrogenated streamobtained from (IIIa) or the bottoms stream obtained from (IIIb) issubjected to (c) as S1.

Thus, the present invention also relates to the process as describedabove, wherein (b) further comprises

-   -   (IIIa) subjecting the stream obtained from (II) to        hydrogenation, obtaining stream S1 and subjecting S1 to step        (c).

Thus, the present invention also relates to the process as describedabove, wherein (b) further comprises

-   -   (IIIb) subjecting the stream obtained from (II) to a        distillation stage, preferably carried out in a distillation        column operated at a top pressure of from 0.7 to 2 bar, more        preferably of from 1.1 to 2 bar, to obtain stream S1 and        subjecting S1 to step (c).

Also, the present invention relates to the process as described above,wherein (b) further comprises

-   -   (IIIa) subjecting the stream S02 obtained from (II) to a        hydrogenation stage, preferably to a catalytical hydrogenation        stage, the catalyst preferably being a heterogeneous catalysts        comprising Ru, Ni, Pd, Pt, either individually or as a mixture        of two or more thereof, as active metal on a suitable support        material, in particular Pd on activated carbon; said        hydrogenation preferably being carried out at a pressure during        hydrogenation in the range of from 1 to 100 bar(abs), preferably        from 1 to 10 bar(abs), and a temperature during hydrogenation in        the range of from 0 to 180° C., preferably from 25 to 120° C.,        more preferably from 65 to 85° C.;    -   (IIIb) subjecting the stream obtained from (IIIa) to a        distillation stage, preferably carried out in a distillation        column operated at a top pressure of from 0.7 to 2 bar, more        preferably of from 1.1 to 2 bar, to obtained stream S1 and        subjecting S1 to step (c).

As mentioned above, it is preferred that the stage (b) of the process ofthe present invention neither comprises (IIIa) nor (IIIb).

Step (c)

According to step (c) of the process of the present invention, thestream S1 is divided into two streams S2 and S3 wherein the stream S3 issubjected, as the part-stream of the present invention, to step (d) asdiscussed hereinunder. The term “is divided into two streams” as used inthis context of the present invention generally encompasses embodimentsaccording to which the stream S1 is divided into more than two streamsprovided that the streams S2 and S3 as defined herein are obtained. Nospecific restrictions exist which portion of S1 is separated as S3.Preferably, the total weight of S3 relative to the total weight of S1 isless than 50%, more preferably less than 40%, more preferably less than30%. More preferably, the total weight of S3 relative to the totalweight of S1 is at least 0.01%. More preferably, the total weight of S3relative to the total weight of S1 is in the range of from 0.01 to 25%.More preferably, the total weight of S3 relative to the total weight ofS1 is in the range of from 0.05 to 20%, preferably from 0.1 to 15%, morepreferably from 0.2 to 10%, more preferably from 0.5 to 7.5%. Preferredconceivable ranges are from 0.5 to 1.5% or from 1.0 to 2.0% or from 1.5to 2.5% or from 2.0 to 3.0% or from 2.5 to 3.5% of from 3.0 to 4.0% orfrom 3.5 to 4.5% or from 4.0 to 5.0% or from 4.5 to 5.5% or from 5.0 to6.0% or from 5.5 to 6.5% or from 6.0 to 7.0% or from 6.5 to 7.5%.

Step (d)

According to step (d) of the process of the present invention, thestream S3 is subjected to a vapor-liquid fractionation in a firstfractionation unit, obtaining a vapor fraction stream S4a beingdepleted, relative to S3, of at least one of the at least one componentB and obtaining a liquid bottoms stream S4b, wherein at least part ofthe vapor fraction stream S4a is subjected to a vapor-liquidfractionation in a second fractionation unit, obtaining a vapor fractionstream S4c and a liquid bottoms stream S4 being depleted, relative toS4a, of at least one of the at least one component B.

Generally, it was found that using for the impurity separation accordingto the present invention a fractionation unit comprising one singledistillation column, already leads to excellent results with regard tomost of the impurities. However, it was found that in view of thecomplexity of the spectrum of the impurities comprised in stream S1,although comprised only in traces, even better results are obtained whentwo serially coupled fractionation units are used. In particular, it wasfound that while the first fractionation unit is especially useful toseparate impurities having a comparatively high boiling point,including, for example, propionitrile, 1-nitropropane, 2-nitropropane,2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol, and/or2,6-dimethyl-4-heptanone, the second fractionation unit is especiallyuseful to separate impurities having a comparatively high boiling point,including, for example acetaldehyde, propionaldehyde or 2-butanone.Thus, using the two serially coupled fractionation units, it waspossible to separate essentially all impurities which, when accumulatingin the course of a continuous process for preparing propylene oxide,tend to have a negative influence on the performance of theheterogeneous catalyst which is preferably employed in the epoxidationprocess, in particular a zeolite-based catalyst having frameworkstructure MWW and containing Ti.

Therefore, the present invention relates to the process as describedabove, wherein in (d), the stream S3 is subjected to a vapor-liquidfractionation in a first fractionation unit, obtaining a vapor fractionstream S4a being depleted, relative to S3, of at least one of the atleast one component B, the at least one of the at least one component Bcomprising propionitrile, or 1-nitropropane, or 2-nitropropane, or2,6-dimethyl-4-heptanol, or 4,6-dimethyl-2-heptanol, or2,6-dimethyl-4-heptanone, or a combination of two, three, four, five, orsix thereof, and obtaining a liquid bottoms stream S4b, wherein at leastpart of the vapor fraction stream S4a is subjected to a vapor-liquidfractionation in a second fractionation unit, obtaining a vapor fractionstream S4c and a liquid bottoms stream S4 being depleted, relative toS4a, of at least one of the at least one component B, the at least oneof the at least one component B comprising acetaldehyde, orpropionaldehyde, or 2-butanone, or a combination of two or threethereof.

The term “S4a being depleted, relative to S3, of at least one of the atleast one component B” as used in this context of the present inventionrelates to a stream S4a in which the amount of the at least one of theat least one component B is lower than the respective amount of the atleast one of the at least one component B in stream S3. The term “S4being depleted, relative to S4a, of at least one of the at least onecomponent B” as used in this context of the present invention relates toa stream S4 in which the amount of the at least one of the at least onecomponent B is lower than the respective amount of the at least one ofthe at least one component B in stream S4a.

Further, the present invention relates to the process as describedabove, wherein in (d), the stream S3, comprising propionitrile,1-nitropropane, 2-nitropropane, 2,6-dimethyl-4-heptanol,4,6-dimethyl-2-heptanol, 2,6-dimethyl-4-heptanone, or a combination oftwo, three, four, five, or six thereof, and further comprisingacetaldehyde, or propionaldehyde, or 2-butanone, or a combination of twoor three thereof, is subjected to a vapor-liquid fractionation in afirst fractionation unit, obtaining a vapor fraction stream S4a beingdepleted, relative to S3, of propionitrile, or 1-nitropropane, or2-nitropropane, or 2,6-dimethyl-4-heptanol, or 4,6-dimethyl-2-heptanol,or 2,6-dimethyl-4-heptanone, or a combination of two, three, four, five,or six thereof, and obtaining a liquid bottoms stream S4b, wherein atleast part of the vapor fraction stream S4a is subjected to avapor-liquid fractionation in a second fractionation unit, obtaining avapor fraction stream S4c and a liquid bottoms stream S4 being depleted,relative to S4a, of acetaldehyde, or propionaldehyde, or 2-butanone, ora combination of two or three thereof.

In particular, it was found that if the configuration of the twoserially coupled fractionation units is used, that in addition to theimpurities having a comparatively high boiling point, including, forexample, propionitrile, 1-nitropropane, 2-nitropropane,2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol, and/or2,6-dimethyl-4-heptanone, other compound having a comparatively lowboiling point including, for example, acetaldehyde, propionaldehyde or2-butanone, can be suitably separated from S3, wherein, relative to S3,the respective amount of such a compound in S4 is in the range of from10 to 70%, preferably from 15 to 60%.

Generally, no specific restrictions exist regarding step (d) providedthat a liquid bottoms stream S4 is obtained which is depleted of the atleast one component B and which can be fed back into the process of thepresent invention. Surprisingly, however, it was found that it isespecially preferred if the acetonitrile concentration of the liquidbottoms stream S4b is in a specific range. This specific range was foundto allow to keep the acetonitrile concentration in the liquid bottomsstream S4b as low as possible, thus avoiding too high a loss ofacetonitrile, and simultaneously to separate a very high amount of theat least one component B via the liquid bottoms stream S4b. Thisspecific range of the concentration of the acetonitrile in the liquidbottoms stream S4b obtained in (d) may be from 1 to 50 weight-%, from 2to 45 weight-%, or from 5 to 40 weight-%. Preferably, in (d),vapor-liquid fractionation is carried out in the first fractionationunit so that from 10 to 30 weight-%, preferably from 10 to 25 weight-%of the liquid bottoms stream S4b consist of acetonitrile. Morepreferably, in (d), vapor-liquid fractionation is carried out in thefirst fractionation unit so that from 10 to 30 weight-%, preferably from10 to 25 weight-% of the liquid bottoms stream S4b consist ofacetonitrile and from 0.1 to 10 weight-%, preferably from 0.25 to 5weight-% of the liquid bottoms stream S4b consist of the at least onefurther component B.

Therefore, the present invention preferably relates to the process asdescribed above, wherein in (c), the total weight of S3 relative to thetotal weight of S1 is in the range of from 0.5 to 7.5% and wherein in(d), vapor-liquid fractionation is carried out in the firstfractionation unit so that from 10 to 25 weight-% of the liquid bottomsstream S4b consist of acetonitrile. More preferably, the presentinvention relates to the process as described above, wherein in (c), thetotal weight of S3 relative to the total weight of S1 is in the range offrom 0.5 to 7.5% and wherein in (d), vapor-liquid fractionation iscarried out in the first fractionation unit so that from 10 to 25weight-% of the liquid bottoms stream S4b consist of acetonitrile andfrom 0.25 to 5 weight-% of the liquid bottoms stream S4b consist of theat least one further component B.

Generally, no specific restrictions exist how the vapor-liquidfractionation is carried out in the first fractionation unit providedthat the above-mentioned acetonitrile concentration in the liquidbottoms stream S4b are achieved. In particular, the pressure and/or thetemperature and/or the number of the theoretical trays of thefractionation unit and/or the reflux ratio will be suitably adjusted bythe skilled person.

Preferably in (d), vapor-liquid fractionation is carried out in thefirst fractionation unit at an absolute pressure at the top of the firstfractionation unit in the range of from 0.5 to 5 bar, more preferablyfrom 0.75 to 2 bar, more preferably from 1 to 1.5.

Preferably, in (d), the number of theoretical trays of the firstfractionation unit is in the range of from 1 to 100, more preferablyfrom 2 to 25, more preferably from 3 to 10.

According to a conceivable embodiment of the present invention, thefirst fractionation unit in (d) is operated with reflux. While it isgenerally possible to use any suitable stream as reflux, it may bepreferred to use a portion of S4a, preferably after condensation, asreflux. The reflux ratio may be in the range of from 0.01:1 to 10:1,such as from 0.1:1 to 5:1, or from 0.5:1 to 2:1. The term “reflux ratio”as used in this context is defined as the ratio of the reflux flowrelative to S4a and is a measure of how much of the material going upthe top of the first fractionation unit is returned back to the firstfractionation unit as reflux.

According to a preferred embodiment of the present invention, the firstfractionation unit in (d) is operated without reflux. According to thisembodiment, it is preferred to feed the stream S3 to the top of thefirst fractionation unit. In this case, it is generally possible tooperate the first fractionation unit as a reboiled stripping unit or asa non-reboiled stripping unit. If the first fractionation unit isdesigned as a reboiled stripping unit, it is preferred that at least oneheat exchanger is suitably arranged at the bottoms of the firstfractionation unit in order to allow for the evaporation of the bottomsstream of the first fractionation unit wherein the stripping vapor isgenerated internally. If the first fractionation unit is designed as anon-reboiled stripping unit, it is preferred that at least one externalvapor feed stream is employed as stripping vapor and to omit the atleast one heat exchanger arranged at the bottoms of the firstfractionation unit. Generally, it is possible to combine at least oneheat exchanger arranged at the bottoms of the first fractionation unitand at least one external vapor feed stream. Preferably, in case thefirst fractionation unit is operated without reflux, the firstfractionation unit is operated as a reboiled stripping unit.

Generally, from 1 to 10%, preferably from 2 to 5% of the stream S3subjected to the first fractionation unit are removed via the liquidbottoms stream S4b. The liquid bottoms stream S4b obtained from thefirst fractionation unit according to (d) generally can be subjected tofurther work-up stages. For example, it is possible to suitably separateacetonitrile from S4b. Further, it may be possible that the liquidbottoms stream comprises or consists of two liquid phases wherein thelower phase which essentially consists of acetonitrile and water can beworked-up to minimize acetonitrile losses in the course of step (d). Ifpresent, the upper organic phase usually made up less than 10 weight-%of the total amount of the bottoms stream. Preferably, the liquidbottoms stream S4b, optionally after further acetonitrile separation, isdiscarded, and since S3 divided from S2 preferably constitutes only aminor portion of S2 which minor portion surprisingly effectivelyprevents the build-up of the concentration of the at least one componentB in the highly integrated process of the present invention, and sinceonly a minor portion of S3 is removed via S4b, simply discarding S4beven without any further work-up is economically advantageous.

Preferably in (d), at least 75 weight-%, more preferably at least 80weight-%, more preferably at least 85 weight-%, more preferably at least90 weight-% of the vapor fraction stream S4a are subjected to thevapor-liquid fractionation in the second fractionation unit. Morepreferably in (d), 95 to 100 weight-%, more preferably from 99 to 100weight-%, more preferably from 99.9 to 100 weight-% of the vaporfraction stream S4a are subjected to the vapor-liquid fractionation inthe second fractionation unit. More preferably, the vapor fractionstream S4a obtained from the first fractionation unit is completelysubjected to the vapor-liquid fractionation in the second fractionationunit.

While it is generally possible to condense at least part of the vaporfraction stream S4a before it is subjected to the second fractionationunit, it is preferred not to condense the vapor fraction stream S4abefore it is subjected to the second fractionation unit.

Generally, there are no specific restrictions where the at least part ofstream S4a is fed to the second fractionation unit. Preferably, the atleast part of stream S4a is fed to the lower part of the secondfractionation unit, preferably to the bottoms of the secondfractionation unit.

Preferably, the second fractionation unit is operated at an absolutepressure in the bottom of the second fractionation unit in the range offrom 65 to 95%, more preferably from 70 to 90, more preferably from 75to 85% of the pressure at the top of the first fractionation unit

Therefore, the present invention relates to the process as definedabove, wherein S3 is fed to the top of the first fractionation unit andthe at least part of the vapor fraction stream S4a is fed to the bottomof the second fractionation unit, wherein in (d), the firstfractionation unit is operated at an absolute pressure at the top of thefirst fractionation unit in the range of from 0.5 to 5 bar, preferablyfrom 0.75 to 2 bar, more preferably from 1 to 1.5 bar, and wherein thesecond fractionation unit is operated at an absolute pressure in thebottom of the second fractionation unit in the range of from 65 to 95%,preferably from 70 to 90, more preferably from 75 to 85% of the pressureat the top of the first fractionation unit.

Preferably, in (d), the number of theoretical trays of the secondfractionation unit is in the range of from 1 to 100, preferably from 3to 50 more preferably from 5 to 30.

According to a preferred embodiment of the present invention, the secondfractionation unit in (d) is operated with reflux. While it is generallypossible to use any suitable stream as reflux, it is preferred to use aportion of S4c, preferably after condensation, as reflux. Preferably,the reflux ratio is in the range of from 0.5:1 to 1:1, more preferablyfrom 0.7:1 to 1:1, more preferably from 0.9:1 to 1:1. The term “refluxratio” as used in this context is defined as the ratio of the refluxflow relative to S4c and is a measure of how much of the material goingup the top of the second fractionation unit is returned back to thesecond fractionation unit as reflux.

According to a conceivable embodiment of the present invention, thesecond fractionation unit in (d) is operated without reflux. Accordingto this embodiment, it is preferred to feed the at least part of thestream S4a to the top of the second fractionation unit. In this case, itis generally possible to operate the second fractionation unit as areboiled stripping unit or as a non-reboiled stripping unit. If thesecond fractionation unit is designed as a reboiled stripping unit, itis preferred that at least one heat exchanger is suitably arranged atthe bottoms of the second fractionation unit in order to allow for theevaporation of the bottoms stream of the second fractionation unitwherein the stripping vapor is generated internally. If the secondfractionation unit is designed as a non-reboiled stripping unit, it ispreferred that at least one external vapor feed stream is employed asstripping vapor and to omit the at least one heat exchanger arranged atthe bottoms of the second fractionation unit. Generally, it is possibleto combine at least one heat exchanger arranged at the bottoms of thesecond fractionation unit and at least one external vapor feed stream.Preferably, in case the second fractionation unit is operated withreflux, the second fractionation unit is operated as a non-reboiledstripping unit.

Therefore, the present invention relates to the process as describedabove, wherein in (d), the first fractionation unit is operated withoutreflux, the at least part of the vapor fraction stream S4a subjected tothe vapor-liquid fractionation in the second fractionation unitpreferably not being condensed prior to subjecting to the vapor-liquidfractionation in the second fractionation unit, and the secondfractionation unit is operated with reflux, wherein a fraction of thevapor fraction stream S4c is used, after condensation, as reflux andwherein the reflux ratio is preferably in the range of from 0.5:1 to1:1, more preferably from 0.7:1 to 1:1, more preferably from 0.9:1 to1:1.

According to the present invention, it is preferred that from 90 to99.99 weight-%, more preferably from 95 to 99.9 weight-%, morepreferably from 98 to 99.9 weight-% of S4 consist of acetonitrile andwater, and that from 0.0001 to 0.2 weight-%, preferably from 0.001 to0.15 weight-%, more preferably from 0.005 to 0.1 weight-% of S4 consistof the at least one component B.

Step (e)

According to step (e) of the process of the present invention, at leasta portion of S4 and at least a portion of S2 are recycled to step (a) ofthe process of the present invention. Generally, it is possible torecycle S4 or the portion thereof without any further work-up stages tostep (a). Preferably, S4 or the portion thereof is subjected to adownstream work-up stage prior to recycling to (a). —Further, accordingto step (e) of the process of the present invention, at least a portionof S2 is recycled to step (a) of the process of the present invention.Generally it is possible to recycle S2 or the portion thereof withoutany further work-up stages to step (a). Preferably, S2 or the portionthereof is subjected to a downstream work-up stage prior to recycling to(a). In case S2 or the portion thereof is subjected to a downstreamwork-up stage prior to recycling to (a), and in case during this work-upstage, the weight ratio of acetonitrile relative to the at least onecomponent B is increased compared to the respective weight ratio of S2,said weight ratio after the work-up stage is lower than the respectiveweight ratio of S4.

Therefore, the present invention relates to the process as describedabove, wherein (e) comprises recycling at least a portion of S4,optionally after work-up, to (a), and recycling at least a portion ofS2, optionally after work-up, to (a).

Preferably, in the work-up stage regarding S4, S4 or the portion thereofis combined with at least a portion of S2. Preferably, in the work-upstage regarding S2, S2 or the portion thereof is combined with at leasta portion of S4. The respectively obtained combined stream is recycled,optionally after work-up, to (a). More preferably, the complete streamS4, optionally after having separated a portion thereof used as refluxto the fractionation unit employed in (d), and the complete stream S2are suitably combined and the combined stream is recycled, optionallyafter work-up, to (a). More preferably, S4 or the portion thereof iscondensed and combined with the stream S2 obtaining a liquid stream.Preferably, the complete stream S4, optionally after having separated aportion thereof used as reflux to the fractionation unit employed in(d), is condensed and combined with S2 obtaining a liquid stream.Preferably, this liquid stream is subjected to a downstream work-upstage prior to recycling to (a).

Therefore, the present invention relates to the process as describedabove, wherein (e) comprises combining at least a portion of S4 and atleast a portion of S2, and recycling the combined stream, optionallyafter work-up, to (a).

According to the present invention, said downstream work-up stageregarding the combined stream preferably comprises an acetonitrile-waterseparation from which separation a stream enriched in acetonitrile isobtained which, optionally after further work-up, is preferably recycledto (a).

Therefore, the present invention relates to the process as describedabove, wherein (e) comprises combining at least a portion of S4 and atleast a portion of S2, subjecting the combined stream to anacetonitrile-water separation obtaining a stream enriched inacetonitrile, and recycling the stream enriched in acetonitrile,optionally after further work-up, to (a).

Therefore, the present invention also relates to the process asdescribed above, wherein (e) comprises working-up S4, said working-upcomprising combining at least a portion of S4, preferably aftercondensation, with S2 obtaining a preferably liquid stream, subjectingsaid preferably liquid stream to acetonitrile-water separation obtaininga stream enriched in acetonitrile, and recycling said stream enriched inacetonitrile, optionally after further work-up, to (a).

Regarding said acetonitrile-water separation, no specific restrictionsexist. Preferably, the acetonitrile-water separation comprises adding astream P preferably comprising at least 95 weight-%, based on the totalweight of P, of C3 wherein C3 is propene optionally admixed withpropane, preferably a liquid stream P,

-   -   either to S2, wherein the resulting stream is combined with at        least the portion of S4 to obtain a preferably liquid stream S5;    -   or to at least the portion of S4, wherein the resulting stream        is combined with S2 to obtain a preferably liquid stream S5;    -   or, preferably, to a liquid stream obtained from combining at        least the portion of S2 and at least the portion of S4.

It is also possible to add a first portion of the stream P to at leastthe portion of S4 and to add a second portion of the stream P to S2 andto combine the two resulting stream to obtain a preferably liquid streamS5. The preferably liquid stream P preferably comprises at least 95weight-%, based on the total weight of P, of C3 wherein C3 is propeneoptionally admixed with propane. Regarding C3, it is preferred that theminimum weight ratio of propene relative to propane of 7:3. In thecontext of the present invention, all embodiments regarding the additionof the stream P described above are encompassed by the term “subjectingthe combined stream to an acetonitrile-water separation obtaining astream enriched in acetonitrile” as used in the context of step (e)above.

Preferably, at least 95 weight-% of P consist of propene or a mixture ofpropene with propane. If P contains a mixture of propene and propane,the weight ratio of propene relative to propane will be at least 7:3.Therefore, propene streams can be employed as P or C3 which have varyingcontents of propane. For example, commercially available propene can beemployed as P or C3 which may be either a polymer grade propene or achemical grade propene. Typically, polymer grade propene will have apropene content of from 99 to 99.8 weight-% and a propane content offrom 0.2 to 1 weight-%. Chemical grade propene will typically have apropene content of from 92 to 98 weight-% and a propane content of from2 to 8 weight-%. According to a preferred embodiment of the presentinvention, a stream P is employed, at least 95 weight-% thereofconsisting of C3, wherein C3 is a mixture of propene and propane and thecontent of C3 regarding propene is in the range of from 92 to 98weight-%, preferably from 94 to 97 weight-%, and the content of C3regarding propane is in the range of from 2 to 8 weight-%, preferablyfrom 3 to 6 weight-%.

As far as the amount of P is concerned, it is preferred that P is addedso that in S5, the weight ratio of C3 relative to acetonitrile is in therange of from 0.2:1 to 5:1, preferably from 0.5 to 1 to 2:1. Therefore,preferably from 90 to 99.9 weight-%, more preferably from 95 to 99.8weight-%, more preferably from 98 to 99.5 weight-% of the stream S5consist of acetonitrile, water and C3, and preferably from 0.01 to 3weight-%, preferably from 0.015 to 2.5 weight-%, more preferably from0.02 to 1.5 weight-% of the stream S5 consist of the at least onecomponent B, wherein the weight ratio of acetonitrile relative to wateris preferably greater than 1:1 and wherein weight ratio of C3 relativeto acetonitrile is preferably in the range of from 0.2:1 to 5:1, morepreferably from 0.5 to 1 to 2:1, wherein regarding C3, the weight ratioof propene relative to propane is at least 7:3.

Preferably, the stream S5 is subjected to a suitably temperature and asuitable pressure by which temperature and pressure treatment two liquidphases L1 and L2 are formed. It was found that it is beneficial for thebreakup into these phases L1 and L2 to subject the stream S5 to as low atemperature as possible with the proviso that the temperature is stillsuitable; for example, the temperature shall not be so low that a solidphase such as ice is formed.

Preferably, the liquid phase L1 enriched in acetonitrile is suitablyseparated from L2 and recycled to (a), optionally after further work-up.Concerning the temperature and pressure treatment, no specificrestrictions exits, provided that the two phases L1 and L2 are formedwherein L1 is enriched in acetonitrile. Preferably, S5 is brought to atemperature of 92° C. at most. According to the present invention, it ispreferred to bring S5 to a temperature in the range of from 5 to 90° C.,preferably from 7- to 80° C., more preferably from 8 to 60° C., morepreferably from 9 to 40° C., and more preferably from 10 to 30° C.Preferably, S5 is subjected to a pressure of at least 10 bar so that S5will be present essentially or completely in its liquid form. The term“essentially in its liquid form” as used in this context of the presentinvention relates to an embodiment according to which at least 95weight-%, more preferably at least 99 weight-% and more preferably atleast 99.9 weight-% of S5 are present in liquid form after beingsubjected to above-mentioned temperatures and pressures. According tothe present invention, it is preferred to subject S5 to a pressure of atleast 15 bar, more preferably to a pressure in the range of from 15 to50 bar, more preferably from 15 to 40 bar, more preferably from 15 to 30bar, and more preferably from 15 to 25 bar.

Bringing S5 to above-mentioned temperature can be accomplished by anysuitable method. According to the present invention, it is preferred touse one or more suitable heat transfer media, e.g. water, in a suitableapparatus, e.g. a shell and tube heat exchanger. Subjecting S5 toabove-mentioned pressure can be accomplished by any suitable method.According to the present invention, it is preferred to use a suitablepump such as a centrifugal pump or a radial pump.

Preferably, at least 95 weight-%, preferably at least 98 weight-% of L1consist of C3, acetonitrile, water and the at least one component B,wherein the water content of L1 is less than 10 weight-%, preferably inthe range of from 1 to 5 weight-%, based on the total weight of L1.

Preferably, at least 98 weight-% of L2 consist of C3, acetonitrile,water and the at least one component B, wherein the C3 content of L2 is5 weight-% at most, based on the total weight of L2, and theacetonitrile content of L2 is less than 45 weight-%, preferably in therange of from 10 to 35 weight-%, based on the total weight of L2.

According to the present invention, temperatures and pressures asdescribed above allow for the existence of two distinct liquid phases L1and L2. Preferably, the two distinct liquid phases L1 and L2 aresuitably separated from each other. Generally, for this separation ofthe two liquid phases, every conceivable method can be applied. Possibleapparatuses used for the separation of L1 from L2 are, for example,gravity settlers, settlers with coalescing aids such as weirs, inclinedplates separator, coalescers such as, for example, mats, beds, layers ofporous or fibrous solids, or membranes, stagewise mixer-settlerequipment, hydrocyclones, centrifuges, suitable columns with or withoutenergy input. Generally, batch mode or continuous mode is conceivable.Preferably, a gravity settler such as vertical or horizontal gravitysettler is employed. Still more preferably, a horizontal gravity settleris employed. It was found that due to the considerable densitydifference and low viscosities achieved for the liquid phases L1 and L2according to the inventive method, the gravity settler, one of thesimplest apparatus, may be employed. According to the present invention,it is conceivable that at least one liquid phase separation improvingagent such as at least one suitable anti-emulsifying, demulsifying oremulsion breaking agent is added. Generally, it is possible to add saidliquid phase separation improving agent to S4 or to S5 or to S4 and S5.The amount of liquid phase separation improving agent added ispreferably at most 1 weight-% based on the total weight of S4 and/or S5.Typically, the amount will be less than 1 weight-%% such as below 0.5weight-% or below 0.1 weight-%. Suitable agents are known by the skilledperson. Reference is made, e.g., to K. J. Lissant, Making and BreakingEmulsions, Res. Lab., Petrolite Corp., St. Louis, Mo., USA, in: K. J.Lissant (ed.), Emulsion Technology (1974), chapter 2, pp 111-124,Dekker, N.Y.; and to S. E. Taylor, Chem. Ind. (1992), pp 770-773.

Therefore, step (e) of the process of the present invention preferablycomprises

-   -   (i) preparing a preferably liquid stream S5 by adding a        preferably liquid stream P to S2, or to at least the portion of        S4, or to the liquid stream obtained from combining S2 and at        least the portion of S4,        -   wherein P comprises at least 95 weight-% of C3, based on the            total weight of P, wherein C3 is propene optionally admixed            with propane with a minimum weight ratio of propene relative            to propane of 7:3, and        -   wherein P is preferably added in an amount so that in S5,            the weight ratio of C3 relative to acetonitrile is in the            range of from 0.2:1 to 5:1, preferably from 0.5:1 to 2:1;    -   (ii) subjecting S5 to a temperature of 92° C. at most and a        pressure of at least 10 bar, preferably to a temperature in the        range of from 5 to 90° C. and a pressure in the range of from 15        to 50 bar, more preferably to a temperature in the range of from        25 to 45° C. and a pressure in the range of from 15 to 25 bar,        obtaining a first liquid phase L1 and a second liquid phase L2,        -   wherein at least 95 weight-%, preferably at least 98            weight-% of L1 consist of C3, acetonitrile, water and the at            least one component B, the water content of L1 being less            than 10 weight-%, preferably in the range of from 1 to 5            weight-%, based on the total weight of L1, and        -   wherein at least 95 weight-%, preferably at least 98            weight-% of L2 consist of C3, acetonitrile, water and the at            least one component B, the C3 content of L2 being 5 weight-%            at most, based on the total weight of L2, and the            acetonitrile content of L2 being less than 45 weight-%,            preferably in the range of from 10 to 35 weight-%, based on            the total weight of L2;    -   (iii) separating L1 from L2, preferably in a gravity settler;    -   (iv) recycling L1 as the stream enriched in acetonitrile,        optionally after further work-up, to (a).

The Stream L2

Preferably, from the process of the present invention, a liquid phase L2is obtained which essentially consists of water and acetonitrile whereinthe weight ratio of acetonitrile:water in L2 is less than 1. The term“essentially consists of acetonitrile and water” as used in this contextof the present invention refers to a liquid phase L2 wherein at least 90weight-% of L2 consist of acetonitrile and water. Preferably, at least95 weight-%, more preferably at least 97 weight-% and still morepreferably at least 98 weight-% of L2 consist of the C3, acetonitrile,and water, wherein the C3 content of L2 is 5 weight-% at most,preferably 3 weight-% at most, and more preferably 2 weight-% at mostbased on the total weight of L2. As far as the acetonitrile isconcerned, the respective content of L2 is preferably less than 45weight-%, more preferably in the range of from 10 to 40 weight-%, morepreferably from 10 to 35 weight-%, based on the total weight of L2.

Generally, the liquid phase L2 can be used in any suitable process. Forexample, it is conceivable that the liquid phase L2 is employed as astream which is passed to an oxidation reaction or a work-up stagedownstream of said oxidation reaction wherein acetonitrile is used assolvent and wherein propene is oxidized, such as an epoxidation reactionwherein acetonitrile is used as solvent and wherein propene is oxidizedby hydrogen peroxide to obtain propylene oxide.

Preferably, the liquid phase L2, prior to being employed in a suitableprocess, is subjected to at least one further separation stage. Apreferred method for said separation comprises subjecting the liquidphase L2 to a distillation stage. Preferably, distillation is carriedout in a suitable manner so that a stream TL2 is obtained which containsfrom 75 to 95 weight-%, preferably from 80 to 85 weight-% acetonitrile,based on the total weight of TL2. Generally, distillation of L2 can becarried out in one, two, or more distillation towers. If thisdistillation is carried out in one distillation tower, the dew-point atthe top of said distillation tower is typically at least 40° C.,preferably in the range of from 40 to 80° C., more preferably in therange of from 40 to 65° C. Typically, the number of theoretical trays isin the range of from 10 to 25. Typical reflux ratios are in the range offrom 0.5 to 3. By such process, stream TL2 is obtained as top streamfrom the distillation tower. The respective bottoms stream, BL2, ispreferably essentially free of acetonitrile. In this context, the term“essentially free of acetonitrile” refers to an embodiment according towhich the acetonitrile content of BL2 is 500 weight-ppm at most,preferably 300 weight-ppm at most, more preferably 100 weight-ppm atmost, based on the total weight of BL2.

Surprisingly, it was found that it is possible to subject liquid phaseL2 to an especially designed distillation stage which allows for ahighly heat-integrated distillation process. Thus, it was found thatseparation of L2 is advantageously carried out using a two pressuredistillation process, wherein in a first distillation tower,distillation is carried out at a top pressure which is higher than thetop pressure of a second distillation tower coupled with said firstdistillation tower, wherein the condenser used to condense the topstream of the first distillation tower is used simultaneously as thevaporizer of the second distillation tower. According to this preferredembodiment, liquid stream L2 is preferably introduced in said firstdistillation tower from which a first bottoms stream and a first topstream are obtained. Preferably, said first distillation tower isoperated at conditions which allow for obtaining a vapor top stream VTL2which contains of from 50 to 70 weight-%, preferably from 55 to 65weight-% of acetonitrile, based on the total weight of VTL2. Typically,said first distillation tower is operated at pressures at the top of thetower in the range of from 10 to 20 bar, preferably from 10 to 15 bar.Generally, the first distillation tower has from 10 to 25, preferablyfrom 15 to 20 theoretical trays. Generally, the reflux ratio of saidfirst distillation tower is in the range of from 0.25:1 to 2:1,preferably of from 0.25:1 to 1:1. The respective bottoms stream obtainedfrom the first distillation tower is preferably essentially free ofacetonitrile. In this context, the term “essentially free ofacetonitrile” refers to an embodiment according to which theacetonitrile content of the bottoms stream of the first distillationtower is 500 weight-ppm at most, preferably 300 weight-ppm at most, morepreferably 100 weight-ppm at most, based on the total weight of thebottoms stream of the first distillation tower. In the following, saidbottoms stream obtained from said first distillation tower, optionallyadmixed with the bottoms stream obtained from the second distillationtower as described hereinunder, is referred to as stream BL2. In thetwo-pressure distillation process, at least a portion of, preferably allof VTL2 is suitably condensed, and this condensed stream is introducedinto the second distillation tower from which a second bottoms streamand a second top stream are obtained. Preferably, said seconddistillation tower is operated at conditions which allow for obtaining atop stream TL2 which contains of from 75 to 95 weight-%, preferably from80 to 85 weight-% of acetonitrile, based on the total weight of TL2.Typically, said second distillation tower is operated at pressures atthe top of the tower in the range of from 1 to 5 bar, preferably from 1to 2 bar. Generally, the second distillation tower has from 8 to 20,preferably from 10 to 15 theoretical trays. Generally, the reflux ratioof said second distillation tower is in the range of from 0.5 to 5,preferably of from 1 to 3. The respective bottoms stream obtained fromthe second distillation tower is preferably essentially free ofacetonitrile. In this context, the term “essentially free ofacetonitrile” refers to an embodiment according to which theacetonitrile content of the bottoms stream of the second distillationtower is 500 weight-ppm at most, preferably 300 weight-ppm at most, morepreferably 100 weight-ppm at most, based on the total weight of thebottoms stream of the second distillation tower.

Preferably, TL2 obtained from the respective distillation tower is atleast partially, preferably completely recycled into the inventiveprocess. More preferably, TL2 is either combined with S4 and/or with S5and/or with P, and optionally also combined with TL1 as describedhereinunder.

If the stream S5 contains at least one propylene glycol, the stream BL2obtained from said distillation preferably contains the at least onepropylene glycol in an amount of from 1 to 5 weight-%, more preferablyin an amount of from 2 to 5 weight-%, based on the total weight of BL2,whereas stream TL2 is essentially free of the at least one propyleneglycol. In this context of the present invention, the term “TL2 isessentially free of the at least one propylene glycol” refers to anembodiment according to which the content of TL2 as to the at least onepropylene glycol is 500 weight-ppm at most TL2 is essentially free ofthe at least one propylene glycol, preferably 200 weight-ppm at most. IfBL2 contains no or essentially no propylene glycol, it is preferred topass BL2 directly to a suitable waste water treatment plant such as abiological waste water treatment plant. It was found that no specifictreatment for the waste water produced by the inventive process isrequired, rendering the process even more cost-efficient andenvironment-friendly. If BL2 contains at least one propylene glycol insignificant amounts, such as in an amount of from 1 to 5 weight-%, morepreferably in an amount of from 2 to 5 weight-%, based on the totalweight of BL2, it can be preferred to pass BL2 to a suitable propyleneglycol separation stage wherein the at least one propylene glycol issuitably separated from water and/or wherein two or more differentpropylene glycols are separate from each other. This process for theseparation of the at least one propylene glycol from BL2 can be carriedout, for example, by evaporating the mixture in at least two, preferablythree evaporation and/or distillation stages, preferably threeevaporation stages, at decreasing operating pressures, preferably in theranges of 1.5 to 5.5 bar at a temperature of 111 to 155° C., followed by1.3 to 5.0 bar at a temperature of 107 to 152° C., followed in turn by0.7 to 4.0 bar at a temperature of 90 to 144° C., thus obtaining mixtureBL2-a and mixture BL2′-b; and separating the mixture BL2-a in at leastone further distillation step, obtaining a mixture BL2-I comprising atleast 70 weight-% of water and a mixture BL2-II comprising less than 30weight-% of water. It is especially preferred to further separatemixture BL2-b into a mixture BL2-Ia comprising at least 90 weight-% ofwater and a mixture BL2-Ib comprising less than 95 weight-% of water bymeans of reverse osmosis. Preferably, the at least one propylene glycolis separated from the mixture BL2-II, preferably admixed with mixtureBL2-Ib, in at least one further distillation step. More preferably,mixtures BL2′-b and BL2-I are combined and further separated intomixture BL2-Ia comprising at least 90 weight-% of water and mixtureBL2-Ib comprising less than 95 weight-% of water by means of reverseosmosis.

Therefore, the present invention also relates to a method as describedabove wherein

-   -   (aa) L2 is introduced into the first distillation tower from        which a vapor top stream VTL2 is obtained containing from 50 to        70 weight-% acetonitrile, based on the total weight of top        stream VTL2, the distillation preferably being carried out at a        top pressure of from 10 to 20 bar; and    -   (bb) at least partially condensing VTL2 obtained in (aa) and        introducing the condensed stream into the second distillation        tower wherefrom TL2 is obtained as top stream, the distillation        preferably being carried out at a top pressure of from 1 to 5        bar,

wherein preferably, the condenser used to condense VTL2 issimultaneously used as vaporizer of the second distillation tower.

The Stream L1

According to the present invention, it is preferred that the stream L1separated according to (iii) is recycled to (a) after further work-up.

Preferably, this further work-up serves for separating C3, preferably aportion of C3, from the acetonitrile. A conceivable method is, forexample, evaporation of the liquid phase L1 by decompression at asuitable pressure. Preferably, the temperature of the liquid phase iskept essentially constant during decompression. By this decompression,C3 is obtained in gaseous form. Thereafter, it is possible to recycle atleast a portion of this gaseous C3 stream, after suitable compression toobtain a liquid stream, for example as at least a portion of stream P.

Preferably, L1 is subjected to fractionation, more preferably todistillation, from which a stream is obtained which is enriched inacetonitrile and which is preferably recycled to (a), optionally after awork-up. Preferably, said stream enriched in acetonitrile is recycled to(a) without further workup. More preferably, this distillation iscarried out in a suitable manner so that a stream TL1 is obtained whichcontains at least 90 weight-%, preferably at least 95 weight-% C3, basedon the total weight of TL1. Preferably according to this distillation, astream BL1 is obtained of which preferably at least 95 weight-%, morepreferably at least 98 weight-% consist of C3, acetonitrile, water andthe at least one component B. More preferably, the C3 content of BL1 isin the range of from 7 to 18 weight-%, preferably from 10 to 15weight-%, in each case based on the total weight of BL1.

Generally, this distillation of L1 can be carried out according to anysuitable method. For example, one, two or more distillation towers canbe employed provided that above-mentioned streams TL1 and BL1 areobtained. Preferably, in said distillation stage, one distillation toweris employed. More preferably, said distillation is carried out at adew-point at the top of said distillation tower of at least 40° C.,preferably in the range of from 40 to 80° C., more preferably in therange of from 40 to 70° C. Preferably, the number of theoretical traysis in the range of from 10 to 20. Preferred reflux ratios are in therange of from 0.01:1 to 0.2:1 such as from 0.05:1 to 0.15:1.

Therefore, the present invention also relates to the process asdescribed above, further comprising working up L1, said working-upcomprising subjecting L1 to a distillation stage wherefrom a bottomsstream BL1 is obtained, wherein at least 95 weight-%, preferably atleast 98 weight-% of BL1 consist of C3, acetonitrile, water and the atleast one component B, wherein the C3 content of BL1 is in the range offrom 7 to 18 weight-%, preferably from 10 to 15 weight-%, and recyclingBL1 as the stream enriched in acetonitrile, optionally after no furtherwork-up, to (a). Preferably, from 0.01 to 5 weight-%, more preferablyfrom 0.015 to 3 weight-%, more preferably from 0.02 to 2 weight-% of BL1consist of the at least one component B. In particular, the distillationtower is operated in a suitable manner, for example by adjusting theenergy input in the sump, which leads to a stream BL1 having a propenecontent which, when being fed back to the epoxidation reaction asrecycling stream, results in a molar ratio of propene relative tohydrogen peroxide in stream (1) in the range of from 0.9:1 to 3.0:1,more preferably from 0.98:1 to 1.6:1, more preferably from 1.0:1 to1.5:1 such as from 1.2:1 to 1.4:1.

Thus, the present invention relates to the process as described above,which process comprises working-up L1 comprising subjecting L1 to adistillation stage wherefrom a bottoms stream BL1 is obtained, whereinat least 95 weight-%, preferably at least 98 weight-% of BL1 consist ofC3, acetonitrile, water and the at least one component B, wherein the C3content of BL1 is in the range of from 7 to 18 weight-%, preferably from10 to 15 weight-%, and recycling BL1 as the stream enriched inacetonitrile, preferably without any further work-up, to (a).

Preferably from 0.01 to 5 weight-%, more preferably from 0.015 to 3weight-%, more preferably from 0.02 to 2 weight-% of BL1 consist of theat least one component B

Further it was found that combining the inventive separation of L1 fromL2 and the downstream separation of TL1 from BL1 allows for a highlyintegrated design of the process of the present invention. On the onehand, stream TL1 is especially suitable for being recycled into theinventive process as at least a portion of P. If, in addition to atleast a portion of TL1, further C3 is added to S1, this further sourceof C3 may be suitably chosen. For example, additional C3 can be added asfresh propene, for example as chemical grade propene containing about 95weight-% propene and about 5 weight-% propane. All other suitablesources of additional C3 are conceivable, such as a C3 stream obtainedfrom a supplier in a Verbund site or the like. Further, it was foundthat the more C3 is recycled via TL1, the more effective the phaseseparation according to (i) to (iii) of the inventive process works interms of as complete a separation of S1 as possible. Therefore, it ispreferred that at least a portion of TL1, preferably all of TL1 isrecycled into (ii).

Generally, it is conceivable that the part-steam distillation may bearranged at another position in the epoxidation downstream process,preferably at a location with access to the acetonitrile solvent stream.

Preferably, such a conceivable location would be a location where theacetonitrile solvent stream is free of or essentially free of propeneand optionally propane, and/or where the acetonitrile solvent stream isfree of or essentially free of hydrogen peroxide. More preferably, sucha conceivable location would be a location downstream the epoxidationreaction step (a) and upstream the location at which the stream P isadmixed, upstream the liquid-liquid separation in (ii). More preferably,such a conceivable location would be a location downstream the locationwhere propylene oxide is removed from the acetonitrile solvent stream instep (b) and upstream the location at which the stream P is admixed,upstream the liquid-liquid separation in (ii). Most preferably, thelocation of the part-stream distillation is the location as describedabove where S3 as a portion of the stream S1 is subjected todistillation. Further, it is generally conceivable that at more than onelocation in the epoxidation downstream process, a part-streamdistillation according to which a portion, preferably a minor portion ofthe acetonitrile solvent stream is subjected to distillation, isarranged.

The present invention is illustrated by the following examples andcomparative examples.

EXAMPLES Example 1: A Preferred Process According to theInvention—General Setup

As to the abbreviations, reference is made to the scheme according toFIGS. 1 and 3, generally described in the section “Description of theFigures” hereinbelow. All pressures given are absolute pressures.

1.1 Preparation of Stream S0 (Step (a))

a) Epoxidation in an Epoxidation Main Reactor (Epoxidation Unit A)

The main reactor A was a vertically mounted tube-bundle reactor with 5tubes (length of the tubes: 12 m, internal tube diameter: 38 mm), eachtube being equipped with an axially placed multi-point thermocouple with10 equally spaced measuring points encased in a suitable thermowell witha diameter of 18 mm. Each tube was charged with 17.5 kg of the ZnTiMWWcatalyst moldings as prepared according to Reference Example 1, section1.8 (post-treated moldings). Free space eventually remaining was filledwith steatite spheres (diameter of 3 mm). The heat of reaction wasremoved by circulating a thermostatized heat transfer medium(water/glycol mixture) on the shell side in co-current to the feed. Theflow rate of the heat transfer medium was adjusted so that thetemperature difference between entrance and exit did not exceed 1° C.The reaction temperature referred to hereinbelow was defined as thetemperature of the heat transfer medium entering the reactor shell. Atthe reactor exit, the pressure was controlled by a pressure regulatorand kept constant at 20 bar.

The reactor was fed from below with a liquid monophasic stream (1).Stream 1 was prepared by mixing four streams (2), (3), (3a) and (4). Thetemperature of stream (1) was not actively controlled, but was usuallyin the range from 20 to 40° C.:

-   -   Stream (2) having a flow rate of 85 kg/h. At least 99.5 weight-%        of stream (2) consisted of acetonitrile, propene and water. This        stream (2) came from the bottoms of the acetonitrile recycle        distillation unit (J).    -   Stream (3) having a flow rate of 15 kg/h was an aqueous hydrogen        peroxide solution having a hydrogen peroxide concentration of 40        weight-% (“crude/washed” grade from Solvay with a TOC in the        range of 100 to 400 mg/kg. The aqueous hydrogen peroxide        solution was supplied from a storage tank, allowing for a        continuous feeding, and fed using a suitable metering pump.    -   Stream (3a) was an aqueous stream comprising dissolved potassium        formate. The further stream was supplied from a storage tank,        allowing for a continuous feeding, and was fed using a suitable        metering pump. The concentration of the potassium formate was        2.5 weight-%, the feed rate of the stream (S3a) was 370 g/h.        Stream (3a) was thoroughly mixed with stream (3) before the        combined stream was mixed with the stream resulting from mixing        stream (2) and (4).    -   Stream (4) was a make-up stream of pure acetonitrile (chemical        grade, from Ineos, purity about 99.9%, containing between 70-180        weight-ppm propionitrile, 5-20 weight-ppm acetamide and less        than 100 weight-ppm water as impurities). Enough fresh        acetonitrile was added to compensate for losses in the process.        Under regular conditions, an average of from 100 to 150 g/h of        make-up acetonitrile were added.

The output stream leaving the epoxidation unit A was sampled every 20minutes in order to determine the hydrogen peroxide concentration usingthe titanyl sulfate method and to calculate the hydrogen peroxideconversion. The hydrogen peroxide conversion was defined as100×(1−m_(out)/m_(in)) wherein m_(in) is the molar flow rate of H₂O₂ inthe reactor feed and m_(out) is the molar flow rate of H₂O₂ in thereactor outlet. Based on the respectively obtained hydrogen peroxideconversion values, the inlet temperature of the heat transfer medium wasadjusted in order to keep the hydrogen peroxide conversion essentiallyconstant in the range of from 90 to 92%. The inlet temperature of theheat transfer medium was set at 30° C. at the start of a given run witha fresh batch of the epoxidation catalyst and was increased, ifnecessary, to maintain the hydrogen peroxide conversion in the mentionedrange. The required temperature increase was usually less than 1 K/d.

b) Intermediate Removal of Propylene Oxide (Distillation Unit B)

After pressure release, the effluent from the epoxidation unit A (stream(5)) was sent to an intermediate propylene oxide removing column(distillation unit B) operated at about 1.1 bar. The column was 6 mhigh, had a diameter of 200 mm and was equipped with 30 bubble trays, anevaporator, and a condenser. The feed to the column entered above bubbletray 25 (counted from the top). The overhead stream leaving the columnwith about 50° C. mainly contained propylene oxide, unconverted propeneand small amounts of oxygen formed as byproduct. This stream was partlycondensed (T=15-25° C.), and the condensed liquid served as an internalreflux stream whereas the gaseous part (stream (6)) was sent to thelights separation column (distillation unit D).

The bottoms temperature of the intermediate propylene oxide removalcolumn was about 80° C. The bottoms stream (stream (7)) was almost freeof propylene oxide (<300 wt.-ppm) and was a mixture of acetonitrile(about 78-80 weight-%), water (about 18-20 weight-%), unconvertedhydrogen epoxide and heavy boilers having a normal boiling point ofabove 100° C., the main heavy boiler being propene glycol. This bottomsstream (7) was subsequently cooled to 35° C. and pumped pump to thefinishing reactor (epoxidation unit C; see section c) below) using asuitable metering pump.

c) Epoxidation in a Finishing Reactor (Epoxidation Unit C)

The total feed stream to the finishing reactor C was obtained by mixingstream (7) obtained according to section b) above with a stream (8) ofpolymer grade liquid propene containing propane (purity about ≥99.5%,feed rate: 0.9 kg/h, at ambient temperature). Both streams (7) and (8)were mixed using a static mixer and fed to the bottom of the finishingreactor C.

The finishing reactor C was a fixed bed reactor operated adiabatically.In this context, the term “adiabatic” refers to an operation modeaccording to which no active cooling is carried out and according towhich the finishing reactor is suitably insulated in order to minimizeheat losses). The finishing reactor C had a length of 4 m and a diameterof 100 mm. The reactor was filled with 9 kg of the same epoxidationcatalyst which was used in the main epoxidation reactor A. Spare spacewas filled with steatite spheres (diameter of 3 mm). The operatingpressure of the finishing reactor C was 10 bar which was kept constantby a suitable pressure regulator at the reactor exit. The output of thefinishing reactor C was sampled every 20 min in order to determine thehydrogen peroxide concentration using the titanyl sulfate method.

The effluent of the finishing reactor C, stream (9), was depressurizedinto a flash drum, and both the liquid and the gas from this drum werefed to a light boiler separation column (distillation unit D).

The stream (6) obtained from the top of the intermediate propylene oxideremoving column (distillation unit B) and the stream (9) obtained aseffluent from the finishing reactor C (epoxidation unit C) togetherconstitute the stream S0 according to the present invention.

This stream S0 had in average an acetonitrile content of from 69 to 70weight-%, a propylene oxide content of 9.8 weight-%, a water content of17 weight-%, a propene content of about 3 weight-%, a propane content ofabout 0.05 weight-%, a hydrogen peroxide content of about 250weight-ppm, a propene glycol content of about 0.1 weight-% and an oxygencontent of about 150 weight-ppm.

1.2 Separation of Propylene Oxide from Stream S0 to Obtain Stream S1(Step (b))

a) Separation of Light Boilers from Streams (6) and (9) (Stream S0) toObtain a Stream (11) (Stream S01 According to Step (I) of the PresentInvention)

The top stream from the intermediate propylene oxide removing column(distillation unit B) (stream (6), see section 1.1 b) above) and thedepressurized outlet stream of the finishing reactor C (stream (9), seesection 1.1 c) above) were sent to a light boiler separation column(distillation unit D) operated at 1.1 bar. The distillation column had alength of 8.5 m, a diameter of 170 mm, and was equipped with 40 bubbletrays, an evaporator at the bottom and a condenser at the top. Thecolumn was operated as a mixed washing/distillation tower. As a washingagent, part of the bottoms stream of distillation unit E (stream 14,about 20-30 kg/h) was taken off, cooled to 10° C. and introduced at thetop of the column. Liquid and gaseous inlet streams were introduced thecolumn at different points. The feed point of the liquid stream (stream(6) plus the liquid portion of stream (9)) was above bubble tray 37; thegaseous stream was introduced into the column above bubble tray 28(counted from the top).

The gaseous stream (10) leaving the cooling means at the top of thecolumn contained mainly propene, propane (which was contained asimpurity in the polymer-grade propene used), oxygen formed as aby-product and small amounts of other light boilers (acetonitrile (about4.7 volume-%), propionaldehyde (about 200 volume-ppm), acetone (about100 volume-ppm, H₂ (about 400 volume-ppm), CO₂ (about 400 volume-ppm)and acetaldehyde (about 100 volume-ppm)), and was essentially free ofpropylene oxide (less than 300 volume-ppm). This top stream was sent tothe flare for disposal.

The bottom stream of the light boiler separation column (stream (11),that is stream S01 of the present invention) having a temperature of 70°C., had a propene content of from 100 to 200 weight-ppm.

b) Separation of Propylene Oxide from Stream (11) (Stream S01) to Obtaina Stream S02 according to Step (II) of the Present Invention

The stream S01 obtained according to section 1.2 a) above was introducedinto a distillation column (distillation unit E) in order to separatepropylene oxide from the stream S01. The column had a height of 50 m anda diameter of 220 mm and was equipped with a packing (Sulzer BX64) witha total packing length of 27.5 m divided into 8 beds with a length of3060 mm each and two beds with a length of 1530 mm each. Between eachbed intermediate flow distributors were installed. The column wasoperated at a top pressure of 750 mbar. The feed point of stream S01 waslocated below the fourth packing bed, counted from the top.

The overhead stream of the column was condensed and partly returned tothe column as reflux (reflux ratio approximately 5:1). The remainder(stream (12)), having a flow rate of 10.1 kg/h, was taken as overheadproduct and essentially consisted of propylene oxide having a purity ofmore than 99.9 weight-%.

The bottoms evaporator was operated in such a way that the propyleneoxide concentration in the bottoms stream was below 100 weight-ppm. Theresulting temperature of the bottoms stream was about 69° C. The streamS02 was then divided in two. The major portion of it (stream (13), witha flow rate of ca. 85 kg/h) was sent to the next distillation column(distillation unit F). The remainder (stream (14), 20-30 kg/h) wascooled and recirculated to the top of the light boiler separation column(distillation unit D) as washing agent as described above in section 1.2a).

This stream S02 had an acetonitrile content of about 80 weight-%, apropylene oxide content of less than 100 wt.-ppm, a water content ofabout 20 weight-%, a propene glycol content of about 0.1 weight-% and ahydroxypropanol content of about 0.1 weight-%.

c) Separation of Light Boiling Compounds from Stream (13) (Stream S02)to Obtain a Stream (16) (Stream S1 according to Step (IIIb) of thePresent Invention)

The stream S02 obtained according to section 1.2 b) above was introducedinto a lights separation column (distillation unit F). This lightsseparation column had a height of 8 m and a nominal diameter of 150 mmand was equipped with 35 bubble trays. The column was operated at a toppressure of 2 bar, and the stream S02 was introduced above bubble traynumber 7 (counted from the bottom).

The overhead stream obtained (stream (15), flow rate about 1 kg/h) leftthe column with a temperature of from 40 to 45° C. and was not condensedas the column was operated with no internal reflux stream. Besidesacetonitrile (6500 vol.-ppm), this overhead stream contained mainlynitrogen which was employed to keep the column operating pressure at avalue of 2 bar) and small amounts of light boilers (acetaldehyde (900vol.-ppm), oxygen (300 vol.-ppm), and propionaldehyde (320 vol.-ppm).This top stream was sent to the flare for disposal.

The sump evaporator was operated by feeding it with a constant amount (5kg/h) of saturated steam at a pressure of 16 bar. The bottom temperatureof the column was 100° C. The bottoms stream, stream S1 of the presentinvention, mainly consisted of acetonitrile and water, the remainderbeing high boilers. This stream S1 had an acetonitrile content of about80 weight-% and a water content of about 20 weight-%.

1.3 Dividing Stream S1 into Streams S2 and S3 (Step (c))

According to present invention, step (c), the stream S1, flow rate 86kg/h, obtained according to section 1.2 c) above, was divided into twostreams, streams S2 (stream (16a according to FIG. 1) and S3 (stream 17according to FIG. 1). Stream S2 had a flow rate of 84 kg/h and stream S3had a flow rate of 2 kg/h. Stream S3, 2.3% of stream S1, was subjectedto part stream distillation unit G (part stream distillation columns).

1.4 Part-Stream Distillation of Stream S1 (Step (d))

The first fractionation unit, i.e. the first distillation column, G1,had a height of 9.5 m and a diameter of 85 mm and was equipped with 6.5meters of metal structured Rombopak 9M packing installed in threeidentical beds. Above the first bed of the structured packing countedfrom the top, the stream S3 ((stream 17)) was introduced in the firstdistillation column. The temperature of the stream S3 stream was 60±3°C. The first distillation column was operated at a top pressure of about1.4 bar and a bottoms temperature of 92±5° C. No reflux was applied. Theamount of steam fed to the bottoms evaporator of the first fractionationunit was controlled in such a way that the concentration of acetonitrilein the bottoms was in the range of from 10 to 25 weight-%. The bottomsstream S4b (stream (18b), about 3% of the stream S3) was removed. Thisstream consisted mainly of water (72-85 weight-%) and acetonitrile(10-24 weight-%). The sum of all the analyzed high-boiling components(27 components) varied in the range of 2-10 weight-%.

The top stream, vapor fraction stream S4a (stream 18a), having atemperature of from 85±3° C., was not condensed and passed to the bottomof the second fractionation unit, i.e. the second distillation column,G2. S4a entered G2 below the last bed of the structured packing countedfrom the top. G2 had a height of 9.5 m and a diameter of 85 mm and wasequipped with 6.5 m of metal structured Rombopak 9M packing installed in3 identical beds. The second distillation column was operated at a toppressure of about 1.25 bar and a bottoms temperature of 85±5° C. The topstream, vapor fraction stream S4c (stream (18c), at most 1% of thestream S4a), was fully condensed by an external overhead condenser (notshown in FIG. 2) and applied essentially completely to use thecondensed, liquid stream as reflux to the second distillation column.The liquid bottoms stream S4 (stream 18), was removed and passed to thenext step (recycling of the stream S4). The stream S4 had anacetonitrile content of about 80 weight-% and a water content of about20 weight-%.

1.5 Recycling of the Stream S4 (Step (4))

a) Preparing a Liquid Stream S5 According to Step (i)

The stream S4, (stream 18 according to FIG. 1 and FIG. 2) was admixedwith stream S2 (stream (16a) according to FIG. 1 and FIG. 2). Thus, thestream S4 was pumped back into the bulk process acetonitrile solventstream. Mixing took place at a point downstream of where stream S3 wasdiverted from stream S1.

This combined stream having a flow rate of 86 kg/h was mixed with aliquid stream P (referred to as stream (23) in FIG. 1 and FIG. 2) toobtain a stream S5. Stream P was fresh propene stream containing propane(polymer grade, purity>96 weight-%, liquefied under pressure, feed rate:10 kg/h).

According to this specific embodiment of the present invention, in orderto obtain the stream S5, the combined stream of S2 and S4 was furthermixed with two other streams: the first one of these streams is stream(19) according to FIG. 1, said stream being obtained from the top of thedistillation unit I. The second one of these streams is stream (22)according to FIG. 1, said stream being obtained from the acetonitrilerecovery unit J. Both streams (19) and (22) are described in detailhereinunder.

b) Adjusting the Temperature of Stream S5 and Separating Liquid PhasesL1 and L2 (Steps (ii) and (iii))

The stream S5 having a flow rate of 150 kg/h±10 kg/h was then fed to amixer-settler unit operated at 18 bar and a temperature in the range of15±5° C. The settler tank had a volume of 5.3 liters. Two liquid phasesL1 and L2 were obtained, an aqueous phase L2 and an organic phase L1.The upper organic phase L1 was removed from the settler tank as stream(20), the lower aqueous phase L2 was removed from the settler tank asstream (21). The stream (20) had a flow rate in the range of 130 kg/h±13kg/h.

The stream (20) then was passed to the acetonitrile recycle unit J, thestream (21) was passed to the acetonitrile recovery unit I from whichthe stream (19) mentioned above was obtained.

The stream (20) thus obtained had an acetonitrile content of about 46weight-%, a propene content of about 51 weight-% and a water content ofabout 3 to 4 weight-%.

The stream (21) thus obtained had an acetonitrile content of about 21weight-%, a water content of about 79 weight-% and a propene content ofless than 0.5 weight-%.

c) Acetonitrile Recovery (Acetonitrile Recovery Unit I)

In order to recycle as much solvent as possible, and in order tominimize acetonitrile losses, the stream (21) was introduced into adistillation column from which the stream (19), also referred to asstream TL2, was obtained as top stream which in turn was recycled intothe solvent stream as described above.

For this purpose, a distillation column with a height of 9.5 m and adiameter of 100 mm, equipped with 50 bubble trays was used. The columnwas operated at a top pressure of 1.5 bar with a reflux ratio of 1:4.Stream (21) was fed to the column above bubble tray 26 (counted from thebottom).

The bottoms temperature was about 113° C., and the bottoms productconsists mainly of water containing high boiling by-products. A typicalcomposition of the bottoms stream was as follows (weight-% given inparenthesis):water (>99.0), propene glycol (0.5), acetonitrile (at most0.001), dipropylene glycol (0.06), acetamide (0.01), acetic acid (0.03),TOC (2.4)). After optional metering and analyzing, this stream wasdiscarded.

The overhead product (stream (19)=stream TL2) had the following typicalcomposition ranges (weight-% given in parenthesis):acetonitrile (75-80),water (15-20), low boilers (e.g. propene, 1). As described above stream(19) is recycled to the feed stream which is passed to the mixer-settlerunit.

d) Acetonitrile Recycling (Acetonitrile Recycling Unit J), Step (iv)

For acetonitrile recycle, the stream (20) obtained from themixer-settler unit H was introduced into a distillation column with aheight of 10 m and a nominal diameter of 200 mm, equipped with 40 bubbletrays. The column was operated at a top pressure of 18 bar with a refluxratio of 1:4. Stream (20) was fed to the column above bubble tray 26(counted from the top). The top product (stream (22)), also referred toas stream TL1, containing mainly propene (ca. 97 vol.-%) with smallamounts of propane (ca. 1-3 vol.-%) was returned to the feed of themixer-settler unit H as described above. Thus, excess propene wasremoved from steam (20) and recycled.

The bottoms stream (stream (2), also referred to as stream BL1), had atemperature in the range of from 106 to 110° C. The precise operationparameters of the column, like energy input in the sump, are adjusted insuch a way that the amount of propene returned to the reactor withstream (2) is in a range such that the molar ratio of propene tohydrogen peroxide in stream (1) was about 1:1.3. For the above mentionedfeed rate of 15 kg/h of aqueous hydrogen peroxide, this means that theconditions needed to be adjusted such that the flow rate of propene instream (2) was about 9.7 kg/h.

Prior to feeding stream (2) to the main epoxidation reactor A,acetonitrile (stream (4), chemical grade, from Ineos, purity about99.9%, containing between 70-180 weight-ppm propionitrile, 5-20weight-ppm acetamide and <100 weight-ppm water as impurities) wasoptionally added to compensate for possible solvent losses. The exactamount of additionally added acetonitrile required depended on thelosses in exit streams and in by-products but also on the number ofsamples taken for analytics. A typical amount of additionally addedacetonitrile for the above-described process design may be in the rangeof from 100 to 150 g/h.

Example 2a: Comparative (without Part-Stream Distillation, withoutHydrogenation)

The process as described above in Example 1 was first taken intooperation using a fresh charge of epoxidation catalyst and freshacetonitrile (same quality as for make-up stream (4), see section 1.5 d)above) but without using the inventive part-stream distillation. Thus,from stream (16) (stream S1), no stream (17) (stream S3) was separatedand subjected to distillation in unit G. Stream 1 was admixed as suchwith streams (19), (22), and (23).

The starting temperature for the cooling medium loop of the epoxidationmain reactor was set at 30° C. At the beginning, the hydrogen peroxideconversion in the epoxidation main reactor A was almost complete. Within24 hours, the hydrogen peroxide conversion started to decrease, and whenit had reached the desired value of approximately 90% (after about100-200 hours), the temperature of the cooling medium was slowly raisedto keep the hydrogen peroxide conversion in the epoxidation main reactorA constant. The rate of the temperature increase of the cooling mediumwas always less than 1° C./day).

The plant was then operated as described above in Example 1 for 441 h.At the end of this period, the temperature of the cooling medium of theepoxidation main reactor was 35° C. At this point, several components(either by-products of the epoxidation reaction and/or impurities in thefeed streams which had not been present at the beginning of the run) hadaccumulated in the solvent loop. The accumulation increased linearlywith no signs of reaching a steady state. The concentration of thecomponents which had accumulated in stream (2), the acetonitrilerecycling stream obtained from unit J, after 441 hours on stream isgiven in Table A. Further, it was found that the stream (2) additionallycontained traces of acetaldehyde, propionaldehyde and 2-butanone whichalso accumulated in the solvent loop, without reaching a steady state.

TABLE A Results of Example 2a Concentration in stream (2) afterComponent 440 hours on stream/weight-ppm propionitrile 444,6-dimethyl-2-heptanol 390 2,6-dimethyl-4-heptanol 8152,6-dimethyl-4-heptanone 14 4,6-dimethyl-2-heptanone 8 1-nitropropane 292-nitropropane 45

This experiment shows that in the absence of the inventive part-streamdistillation, the overall process including solvent recycling suffersfrom an accumulation of several compounds in the solvent loop. Nosteady-state was reached relative to the concentration of thesecompounds.

Example 2b: According to the Invention (with Part-Stream Distillation,without Hydrogenation

The run as described in Example 2a was continued, and at t=441 hours onstream, the part-stream distillation (unit G, with the firstdistillation column G1 and the second distillation column G2) was takeninto operation. The run was then continued until a time on stream of1800 hours was reached. During this period, a stream S3 with a constantflow rate of 2 kg/h (±0.1 kg/h) was diverted from the stream S1 and fedto unit G, corresponding to about 2.3% of the total amount of stream S1.A bottoms stream S4b (stream 18b)) with a constant flow rate of 40 g/h(±10 g/h) was removed at the bottom of the distillation column G1 anddiscarded. The composition of this bottoms stream after 1800 hours onstream was as follows (weight-% in parenthesis):water (77.5), propeneglycol (6.1), acetonitrile (14.1), dipropylene glycol (0.20),tripropylene glycol (0.12), acetamide (0.16), 2,6-dimethyl-4-heptanol(0.16), 4,6-dimethyl-2-heptanol (0.08), 1-nitropropane (0.004),2-nitropropane (0.004), hydroxyacetone (0.4), acetic acid (0.6), ammonia(0.02), TOC (0.02), acid value=1.4 mg/g (determined according to DIN ENISO 2114). The concentration of the impurities in the solvent loop (instream (2) just before starting the part-stream distillation (at 441hours on stream) and at the end of the run with part-stream distillation(after 1329 hours on stream) is given in Table B.

TABLE B Results of Example 2b Concentration in stream (2)/weight-ppmBefore starting the part-stream At the end distillation (at of the run(at Stationary 440 hours 1800 hours since/hours Component on stream) onstream) on stream propionitrile 44 26 a) 4,6-dimethyl-2-heptanol 346 481700 2,6-dimethyl-4-heptanol 722 20 a) 2,6-dimethyl-4-heptanone 13 21700 4,6-dimethyl-2-heptanone 7 2 1700 1-nitropropane 26 4  9502-nitropropane 40 8  950 a) Concentration of this component was stillfalling when the experiment was finished.

At the end of the run, all respective concentrations in stream (2),including the concentrations of acetone, acetaldehyde, propionaldehydeand 2-butanone, not listed in Table B, had reached steady-state, and noaccumulation was observed any more. This inventive example clearly showsthat making use of the inventive part-stream distillation according towhich only a minor fraction of the stream S1 is separated and subjectedto distillation, the accumulation of by-products and impurities duringsolvent recycling can be stopped and a steady-state at very lowconcentration levels can be reached. Yet further, the example shows thatthe inventive part-stream distillation method even allows tosignificantly reduce the concentration of by-products and impuritiesaccumulated in the acetonitrile solvent loop. It also shows that it issufficient to work-up a small side stream to obtain the desired result,thus offering large savings in energy and investment.

Example 3a: Comparative (without Part-Stream Distillation, withHydrogenation)

In a new run, the process as described above in Example 1 was firsttaken into operation using a fresh charge of epoxidation catalyst andfresh acetonitrile (same quality as for make-up stream (4), see section1.5 d) above) but without using the inventive part-stream distillation.Thus, from stream (16) (stream S1), no stream (17) (stream S3) wasdiverted and subjected to distillation in unit G. Stream 1 was admixedas such with streams (19), (22), and (23).

In this example, stream (13) (steam S02)) was passed through ahydrogenation reactor (not shown in FIG. 1) located downstream the unitE and upstream the unit F. The hydrogenation reactor was a tubularreactor with a diameter of 53 mm and a height of 3.25 m, filled with afixed bed catalyst (0.3 weight-% Pd on Al₂O₃, strands with 4 mmdiameter, HO-13 S4 from BASF SE, operated adiabatically. The reactor wasoperated as a packed bubble column with gas and liquid flowing inco-current from the bottom to the top of the reactor at a pressure ofabout 15 bar. Hydrogen was provided was fed at a constant rate of 100g/h. The temperature of the liquid feed stream (13) to the hydrogenationreactor was adjusted to 70° C. and kept constant throughout the run. Atthe hydrogenation reactor exit, the pressure was reduced to 1 bar, andthe liquid phase and the gas phase leaving the hydrogenation reactorwere separated. The gaseous phase was discarded and the liquid phase wasfed to unit F as described hereinabove.

The starting temperature for the cooling medium loop of the epoxidationmain reactor A was set at 30° C. At the beginning, the hydrogen peroxideconversion in the epoxidation main reactor was almost complete. Within24 hours, the hydrogen peroxide conversion started to decrease, and whenit had reached the desired value of approximately 90% (after about100-200 hours) the temperature of the cooling medium was slowly raisedto keep the hydrogen peroxide conversion in the epoxidation main reactorA constant. The rate of the temperature increase of the cooling mediumwas always less than 1° C./day).

The plant was then operated as described above in Example 1 for 864 h.At the end of this period, the temperature of the cooling medium of theepoxidation main reactor was 39.2° C. At this point, several components(either by-products of the epoxidation reaction and/or impurities in thefeed streams which had not been present at the beginning of the run) hadaccumulated in the solvent loop. The accumulation increased linearlywith no signs of reaching a steady state. The concentration of thecomponents which had accumulated in stream (2), the acetonitrilerecycling stream obtained from unit J, after 864 hours on stream isgiven in Table C. Further, it was found that the stream (2) additionallycontained traces of acetone, acetaldehyde, propionaldehyde and2-butanone which also accumulated in the solvent loop, without reachinga steady state.

TABLE C Results of Example 3a Concentration in stream (2) afterComponent 864 hours on stream/weight-ppm propionitrile 2374,6-dimethyl-2-heptanol 1121 2,6-dimethyl-4-heptanol 21682,6-dimethyl-4-heptanone 23 4,6-dimethyl-2-heptanone 20 1-nitropropane204 2-nitropropane 229

This experiment shows that in the absence of the inventive part-streamdistillation, the overall process including solvent recycling suffersfrom an accumulation of several compounds in the solvent loop. Nosteady-state was reached relative to the concentration of thesecompounds.

Example 3b: According to the Invention (with Part-Stream Distillation,with Hydrogenation)

The run as described in Example 3a was continued, and at t=864 hours onstream, the part-stream distillation (unit G) was taken into operation.The run was then continued until a time on stream of 1600 hours wasreached.

During this period, a stream S3 with a constant flow rate of 2 kg/h(±0.1 kg/h) was diverted from the stream S1 and fed to the distillationunit G, corresponding to about 2.3% of the total amount of stream S1. Abottoms stream with a constant flow rate of 50 g/h was removed at thebottom of the distillation column G1 and, after being analyzed, wasdiscarded.

The composition of the stream S2 after reaching steady-state was asfollows: water (76.1), propene glycol (0.43), propionitrile (0.11),acetonitrile (14.1), dipropylene glycol (0.20), tripropylene glycol(0.13), acetamide (0.17), 2,6-dimethyl-4-heptanol (0.14),4,6-dimethyl-2-heptanol (0.12), 1-nitropropane (0.10), 2-nitropropane(0.11), hydroxyacetone (0.34), acetic acid (0.46), ammonia (0.03), TOC(0.02), acid value=1.4 mg/g.

The concentration of the impurities in the solvent loop (in stream (2)just before starting the part-stream distillation (at 864 hours onstream) and at the end of the experiment (after 1600 hours on stream) isgiven in Table D.

TABLE D Results of Example 3b Concentration in stream (2)/weight-ppmBefore starting the part-stream At the end distillation (at of the run(at 864 hours 1600 hours Component on stream) on stream) propionitrile237 139 4,6-dimethyl-2-heptanol 1121 370 2,6-dimethyl-4-heptanol 2168783 2,6-dimethyl-4-heptanone 25 9 4,6-dimethyl-2-heptanone 20 51-nitropropane 204 87 2-nitropropane 232 107

Between 1370-1580 hours on stream, all the concentrations in stream (2),including the concentrations of acetone, acetaldehyde, propionaldehydeand 2-butanone, not listed in Table D, had reached steady-state, and noaccumulation was observed any more. Until the end of the run noaccumulation was observed any more.

This inventive example clearly shows that making use of the inventivepart-stream distillation according to which only a minor fraction of thestream S1 is separated and subjected to distillation, the accumulationof by-products and impurities during solvent recycling can be stoppedand a steady-state at very low concentration levels can be reached. Yetfurther, the example shows that the inventive part-stream distillationmethod even allows to significantly reduce the concentration ofby-products and impurities accumulated in the acetonitrile solvent loop.It also shows that it is sufficient to work-up a small side stream toobtain the desired result, thus offering large savings in energy andinvestment.

Reference Example 1: Preparation of the Epoxidation Catalyst (ZnTiMWW)

1.1 Preparation of Boron-Containing MWW

470.4 kg de-ionized water were provided in a vessel. Under stirring at70 rpm (rounds per minute), 162.5 kg boric acid were suspended in thewater. The suspension was stirred for another 3 h. Subsequently, 272.5kg piperidine were added, and the mixture was stirred for another hour.To the resulting solution, 392.0 kg Ludox® AS-40 were added, and theresulting mixture was stirred at 70 rpm for another hour. The finallyobtained mixture was transferred to a crystallization vessel and heatedto 170° C. within 5 h under autogenous pressure and under stirring (50rpm). The temperature of 170° C. was kept essentially constant for 120h; during these 120 h, the mixture was stirred at 50 rpm. Subsequently,the mixture was cooled to a temperature of from 50-60° C. within 5 h.The aqueous suspension containing B-MWW had a pH of 11.3 as determinedvia measurement with a pH electrode. From said suspension, the B-MWW wasseparated by filtration. The filter cake was then washed with de-ionizedwater until the washing water had a conductivity of less than 700microSiemens/cm. The thus obtained filter cake was subjected tospray-drying in a spray-tower with the following spray-dryingconditions:

drying gas, nozzle gas: technical nitrogen

temperature drying gas:

-   -   temperature spray tower (in): 288-291° C.    -   temperature spray tower (out): 157-167° C.    -   temperature filter (in): 150-160° C.    -   temperature scrubber (in): 40-48° C.    -   temperature scrubber (out): 34-36° C.

pressure difference filter: 8.3-10.3 mbar

nozzle:

-   -   top-component nozzle supplier Gerig; size 0    -   nozzle gas temperature: room temperature    -   nozzle gas pressure: 2.5 bar

operation mode: nitrogen straight

apparatus used: spray tower with one nozzle

configuration: spray tower—filter—scrubber

gas flow: 1,900 kg/h

filter material: Nomex® needle-felt 20 m²

dosage via flexible tube pump: SP VF 15 (supplier: Verder)

The spray tower was comprised of a vertically arranged cylinder having alength of 2,650 mm, a diameter of 1,200 mm, which cylinder was conicallynarrowed at the bottom. The length of the conus was 600 mm. At the headof the cylinder, the atomizing means (a two-component nozzle) werearranged. The spray-dried material was separated from the drying gas ina filter downstream of the spray tower, and the drying gas was thenpassed through a scrubber. The suspension was passed through the inneropening of the nozzle, and the nozzle gas was passed through thering-shaped slit encircling the opening. The spray-dried material wasthen subjected to calcination at 650° C. for 2 h. The calcined materialhad a boron (B) content of 1.9 weight-%, a silicon (Si) content of 41weight-%, and a total organic carbon (TOC) content of 0.18 weight-%.

1.2 Preparation of Deboronated MWW

Based on the spray-dried material obtained according to section 1.1above, 4 batches of deboronated zeolite MWW were prepared. In each ofthe first 3 batches, 35 kg of the spray-dried material obtainedaccording to section 1.1 and 525 kg water were employed. In the fourthbatch, 32 kg of the spray-dried material obtained according to section1.1 and 480 kg water were employed. In total, 137 kg of the spray-driedmaterial obtained according to section 1.1 and 2025 kg water wereemployed. For each batch, the respective amount of water was passed intoa vessel equipped with a reflux condenser. Under stirring at 40 r.p.m.,the given amount of the spray-dried material was suspended into thewater. Subsequently, the vessel was closed and the reflux condenser putinto operation. The stirring rate was increased to 70 r.p.m. Understirring at 70 r.p.m., the content of the vessel was heated to 100° C.within 10 h and kept at this temperature for 10 h. Then, the content ofthe vessel was cooled to a temperature of less than 50° C. The resultingdeboronated zeolitic material of structure type MWW was separated fromthe suspension by filtration under a nitrogen pressure of 2.5 bar andwashed four times with deionized water. After the filtration, the filtercake was dried in a nitrogen stream for 6 h. The deboronated zeoliticmaterial obtained in 4 batches (625.1 kg nitrogen-dried filter cake intotal) had a residual moisture content of 79%, as determined using an IR(infrared) scale at 160° C. From the nitrogen-dried filter cake having aresidual moisture content of 79% obtained according to section a) above,an aqueous suspension was prepared with deionized water, the suspensionhaving a solid content of 15 weight-%. This suspension was subjected tospray-drying in a spray-tower with the following spray-dryingconditions:

drying gas, nozzle gas: technical nitrogen

temperature drying gas:

-   -   temperature spray tower (in): 304° C.    -   temperature spray tower (out): 147-150° C.    -   temperature filter (in): 133-141° C.    -   temperature scrubber (in): 106-114° C.    -   temperature scrubber (out): 13-20° C.

pressure difference filter: 1.3-2.3 mbar

nozzle:

-   -   top-component nozzle: supplier Niro, diameter 4 mm    -   nozzle gas throughput: 23 kg/h    -   nozzle gas pressure: 2.5 bar

operation mode: nitrogen straight

apparatus used: spray tower with one nozzle

configuration: spray tower—filter—scrubber

gas flow: 550 kg/h

filter material: Nomex® needle-felt 10 m²

dosage via flexible tube pump: VF 10 (supplier: Verder)

The spray tower was comprised of a vertically arranged cylinder having alength of 2,650 mm, a diameter of 1,200 mm, which cylinder was conicallynarrowed at the bottom. The length of the conus was 600 mm. At the headof the cylinder, the atomizing means (a two-component nozzle) werearranged. The spray-dried material was separated from the drying gas ina filter downstream of the spray tower, and the drying gas was thenpassed through a scrubber. The suspension was passed through the inneropening of the nozzle, and the nozzle gas was passed through thering-shaped slit encircling the opening. The spray-dried MWW materialobtained had a B content of 0.08 weight-%, an Si content of 42 weight-%,and a TOC of 0.23 weight-%.

1.3 Preparation of TiMWW

Based on the deboronated MWW material as obtained according to section1.2 above, a zeolitic material of structure type MWW containing titanium(Ti) was prepared, referred to in the following as TiMWW. The synthesiswas performed in two experiments, described in the following as a) andb):

a) First Experiment

Starting materials: deionized water: 244.00 kg piperidine: 118.00 kgtetrabutylorthotitanate: 10.90 kg deboronated zeolitic material: 54.16kg

54.16 kg of the deboronated zeolitic material of structure type MWW weretransferred in to a first vessel A. In a second vessel B, 200.00 kgdeionized water were transferred and stirred at 80 r.p.m. 118.00 kgpiperidine were added under stirring, and during addition, thetemperature of the mixture increased for about 15° C. Subsequently,10.90 kg tetrabutylorthotitanate and 20.00 kg deionized water wereadded. Stirring was then continued for 60 min. The mixture of vessel Bwas then transferred into vessel A, and stirring in vessel A was started(70 r.p.m.). 24.00 kg deionized water were filled into vessel A andtransferred to vessel B. The mixture in vessel B was then stirred for 60min. at 70 r.p.m. At the beginning of the stirring, the pH of themixture in vessel B was 12.6, as determined with a pH electrode. Aftersaid stirring at 70 r.p.m., the frequency was decreased to 50 r.p.m.,and the mixture in vessel B was heated to a temperature of 170° C.within 5 h. At a constant stirring rate of 50 r.p.m., the temperature ofthe mixture in vessel B was kept at an essentially constant temperatureof 170° C. for 120 h under autogenous pressure. During thiscrystallization of TiMWW, a pressure increase of up to 10.6 bar wasobserved. Subsequently, the obtained suspension containing TiMWW havinga pH of 12.6 was cooled within 5 h. The cooled suspension was subjectedto filtration, and the separated mother liquor was transferred to wastewater discharge. The filter cake was washed four times with deionizedwater under a nitrogen pressure of 2.5 bar. After the last washing step,the filter cake was dried in a nitrogen stream for 6 h. From 246 kg ofsaid filter cake, an aqueous suspension was prepared with deionizedwater, the suspension having a solid content of 15 weight-%. Thissuspension was subjected to spray-drying in a spray-tower with thefollowing spray-drying conditions:

drying gas, nozzle gas: technical nitrogen

temperature drying gas:

-   -   temperature spray tower (in): 304° C.    -   temperature spray tower (out): 147-152° C.    -   temperature filter (in): 133-144° C.    -   temperature scrubber (in): 111-123° C.    -   temperature scrubber (out): 12-18° C.

pressure difference filter: 1.8-2.8 mbar

nozzle:

-   -   top-component nozzle: supplier Niro, diameter 4 mm    -   nozzle gas throughput: 23 kg/h    -   nozzle gas pressure: 2.5 bar

operation mode: nitrogen straight

apparatus used: spray tower with one nozzle

configuration: spray tower—filter—scrubber

gas flow: 550 kg/h

filter material: Nomex® needle-felt 10 m²

dosage via flexible tube pump: VF 10 (supplier: Verder)

The spray tower was comprised of a vertically arranged cylinder having alength of 2,650 mm, a diameter of 1,200 mm, which cylinder was conicallynarrowed at the bottom. The length of the conus was 600 mm. At the headof the cylinder, the atomizing means (a two-component nozzle) werearranged. The spray-dried material was separated from the drying gas ina filter downstream of the spray tower, and the drying gas was thenpassed through a scrubber. The suspension was passed through the inneropening of the nozzle, and the nozzle gas was passed through thering-shaped slit encircling the opening. The spray-dried TiMWW materialobtained from the first experiment had a Si content of 37 weight-%, a Ticontent of 2.4 weight-%, and a TOC of 7.5 weight-%.

b) Second Experiment

The second experiment was carried out in the same way as the firstexperiment described in section a) above. The spray-dried TiMWW materialobtained from the second experiment had a Si content of 36 weight-%, aTi content of 2.4 weight-%, a TOC of 8.0 weight-%

1.4 Acid Treatment of TiMWW

Each of the two spray-dried TiMWW materials as obtained in the first andthe second experiment described in sections 1.3 a) and 1.3 b) above wassubjected to acid treatment as described in the following in sections a)and b). In section c) hereinunder, it is described how a mixture of thematerials obtained from a) and b) are spray-dried. In section d)hereinunder, it is described how the spray-dried material is calcined.

a) Acid Treatment of the Spray-Dried Material Obtained According toSection 1.3.a)

Starting materials: deionized water: 690.0 kg nitric acid: (53%): 900.0kg spray-dried Ti-MWW 1.3. a): 53.0 kg

670.0 kg deionized water were filled in a vessel. 900 kg nitric acidwere added, and 53.0 kg of the spray-dried TiMWW were added understirring at 50 r.p.m. The resulting mixture was stirred for another 15min. Subsequently, the stirring rate was increased to 70 r.p.m. Within 1h, the mixture in the vessel was heated to 100° C. and kept at thistemperature and under autogenous pressure for 20 h under stirring. Thethus obtained mixture was then cooled within 2 h to a temperature ofless than 50° C. The cooled mixture was subjected to filtration, and thefilter cake was washed six times with deionized water under a nitrogenpressure of 2.5 bar. After the last washing step, the filter cake wasdried in a nitrogen stream for 10 h. The washing water after the sixthwashing step had a pH of about 2.7. 225.8 kg dried filter cake wereobtained.

b) Acid Treatment of the Spray-Dried Material Obtained According toSection 1.3.b)

Starting materials: deionized water: 690.0 kg nitric acid: (53%): 900.0kg spray-dried Ti-MWW 1.3. b): 55.0 kg

The acid treatment of the spray-dried material obtained according tosection 1.3.b) was carried in the same way as the acid treatment of thespray-dried material obtained according to section 1.3.a) as describedin section 1.4 a). The washing water after the sixth washing step had apH of about 2.7. 206.3 kg dried filter cake were obtained.

c) Spray-Drying of the Mixture of the Materials Obtained from 1.4.a) and1.4 b)

From 462.1 kg of the mixture of the filter cakes obtained from 1.4.a)and 1.4 b), an aqueous suspension was prepared with deionized water, thesuspension having a solid content of 15 weight-%. This suspension wassubjected to spray-drying in a spray-tower with the followingspray-drying conditions:

drying gas, nozzle gas: technical nitrogen

temperature drying gas:

-   -   temperature spray tower (in): 304-305° C.    -   temperature spray tower (out): 151° C.    -   temperature filter (in): 141-143° C.    -   temperature scrubber (in): 109-118° C.    -   temperature scrubber (out): 14-15° C.

pressure difference filter: 1.7-3.8 mbar

nozzle:

-   -   top-component nozzle: supplier Niro, diameter 4 mm    -   nozzle gas throughput: 23 kg/h    -   nozzle gas pressure: 2.5 bar

operation mode: nitrogen straight

apparatus used: spray tower with one nozzle

configuration: spray tower—filter—scrubber

gas flow: 550 kg/h

filter material: Nomex® needle-felt 10 m²

dosage via flexible tube pump: VF 10 (supplier: Verder)

The spray tower was comprised of a vertically arranged cylinder having alength of 2,650 mm, a diameter of 1,200 mm, which cylinder was conicallynarrowed at the bottom. The length of the conus was 600 mm. At the headof the cylinder, the atomizing means (a two-component nozzle) werearranged. The spray-dried material was separated from the drying gas ina filter downstream of the spray tower, and the drying gas was thenpassed through a scrubber. The suspension was passed through the inneropening of the nozzle, and the nozzle gas was passed through thering-shaped slit encircling the opening. The spray-dried acid-treatedTiMWW material had a Si content of 42 weight-%, a Ti content of 1.6weight-%, and a TOC content of 1.7 weight-%.

d) Calcination of the Spray-Dried Material Obtained According to 1.4.c)

The spray-dried material was then subjected to calcination at 650° C. ina rotary furnace for 2 h. The calcined material had a Si content of 42.5weight-%, a Ti content of 1.6 weight-% and a TOC content of 0.15weight-%.

1.5 Impregnation of TiMWW with Zn

The acid-treated, spray-dried and calcined material as obtainedaccording to 1.4 d) was then subjected to an impregnation stage.

Starting materials: deionized water: 2610.0 kg zinc acetate dihydrate:15.93 kg calcined Ti-MWW 1.4.d): 87.0 kg

Impregnation was carried out in 3 batches a) to c) as follows:

-   -   a) In a vessel equipped with a reflux condenser, a solution of        840 kg deionized water and 5.13 kg zinc acetate dihydrate was        prepared within 30 min. Under stirring (40 r.p.m.), 28 kg of the        calcined Ti-MWW material obtained according to 1.4.d) were        suspended. Subsequently, the vessel was closed and the reflux        condenser put into operation. The stirring rate was increased to        70 r.p.m.    -   b) In a vessel equipped with a reflux condenser, a solution of        840 kg deionized water and 5.13 kg zinc acetate dihydrate was        prepared within 30 min. Under stirring (40 r.p.m.), 28 kg of the        calcined Ti-MWW material obtained according to 1.4.d) were        suspended. Subsequently, the vessel was closed and the reflux        condenser put into operation. The stirring rate was increased to        70 r.p.m.    -   c) In a vessel equipped with a reflux condenser, a solution of        930 kg deionized water and 5.67 kg zinc acetate dihydrate was        prepared within 30 min. Under stirring (40 r.p.m.), 31 kg of the        calcined Ti-MWW material obtained according to 1.4.d) were        suspended. Subsequently, the vessel was closed and the reflux        condenser put into operation. The stirring rate was increased to        70 r.p.m.

In all batches a) to c), the mixture in the vessel was heated to 100° C.within 1 h and kept under reflux for 4 h a t a stirring rate of 70r.p.m. Then, the mixture was cooled within 2 h to a temperature of lessthan 50° C. For each batch a) to c), the cooled suspension was subjectedto filtration, and the mother liquor was transferred to waste waterdischarge. The filter cake was washed five times with deionized waterunder a nitrogen pressure of 2.5 bar. After the last washing step, thefilter cake was dried in a nitrogen stream for 10 h. For batch a), 106.5kg nitrogen-dried filter cake were finally obtained. For batch b), 107.0kg nitrogen-dried filter cake were finally obtained. For batch c), 133.6kg nitrogen-dried filter cake were finally obtained. The thus driedZn-impregnated TiMWW material (ZnTiMWW), for each batch, had a Sicontent of 42 weight-%, a Ti content of 1.6 weight-%, a Zn content of1.4 weight-% and a TOC of 1.4 weight-%.

1.6 Preparation of a Micropowder

From 347.1 kg of the mixture of the filter cakes obtained according to1.5 above, an aqueous suspension was prepared with deionized water, thesuspension having a solid content of 15 weight-%. This suspension wassubjected to spray-drying in a spray-tower with the followingspray-drying conditions:

-   -   apparatus used: spray tower with one nozzle    -   operation mode: nitrogen straight    -   configuration: dehumidifier—filter—scrubber    -   dosage: flexible-tube pump VF 10 (supplier: Verder) nozzle with        a diameter of 4 mm (supplier: Niro)    -   filter material: Nomex® needle-felt 10 m²

Runtime/h 0.5 1.5 2.5 3.5 4.5 Flow rate gas/(kg/h) 550 550 550 550 550Temperature spray tower (in) 305 305 305 305 305 drying gas/° C. spraytower (out) 151 151 151 151 151 Filter (in) 140 137 130 127 126 Scrubber(in) 110 110 110 108 105 Scrubber (out) 14 14 15 15 15 Differentialspray tower 3.1 3 3 2.8 2.9 pressure/mbar Filter 1.7 1.7 1.8 1.8 2.1Scrubber 3.8 4.1 4.2 4.2 4.2 Pressure/mbar spray tower −103 −1.2 −0.9−0.9 −1.1 Nozzle gas Flow rate kg/h 23 23 23 23 23 Temperature/° C.r.t.*) r.t.*⁾ r.t.*⁾ r.t.*⁾ r.t.*) Pressure/bar 2.5 2.5 2.5 2.5 2.5Spray-dried Temperature/° C. r.t.*) r.t.*) r.t.*) r.t.*) r.t.*) product*)room temperature

The spray tower was comprised of a vertically arranged cylinder having alength of 2,650 mm, a diameter of 1,200 mm, which cylinder was conicallynarrowed at the bottom. The length of the conus was 600 mm. At the headof the cylinder, the atomizing means (a two-component nozzle) werearranged. The spray-dried material was separated from the drying gas ina filter downstream of the spray tower, and the drying gas was thenpassed through a scrubber. The suspension was passed through the inneropening of the nozzle, and the nozzle gas was passed through thering-shaped slit encircling the opening. The spray-dried material thusobtained had a Zn content of 1.4 weight-%, a Ti content of 1.7 weight-%,a Si content of 40 weight-%, and a TOC content of 0.27 weight-%. Thespray-dried product was then subjected to calcination for 2 h at 650° C.under air in a rotary furnace, yielding 76.3 kg of calcined spray-driedZnTiMWW. The calcined spray-dried material thus obtained had a Zncontent of 1.4 weight-%, a Ti content of 1.7 weight-%, a Si content of42 weight-%, and a C content of 0.14 weight-%. The bulk density of thecalcined spray-dried ZnTiMWW was 90 g/I (gram/liter).

1.7 Preparation of a Molding

Starting from the calcined spray-dried ZnTiMWW material obtainedaccording to section 1.6 above, a molding was prepared, dried, andcalcined. Therefor, 22 batches were prepared, each starting from 3.4 kgof the calcined spray-dried ZnTiMWW material obtained in Example 1,0.220 kg Walocel™ (Walocel MW 15000 GB, Wolff Cellulosics GmbH & Co. KG,Germany), 2.125 kg Ludox® AS-40 and 6.6 l deionized water, as follows:3.4 kg ZnTiMWW and 0.220 kg Walocel were subjected to kneading in anedge mill for 5 min. Then, during further kneading, 2.125 kg Ludox wereadded continuously. After another 10 min, addition of 6 l of deionizedwater was started. After another 30 min, further 0.6 l of deionizedwater were added. After a total time of 50 min, the kneaded mass hadbecome extrudable. Thereafter, the kneaded mass was subjected toextrusion under 65-80 bar wherein the extruder was cooled with waterduring the extrusion process. Per batch, the extrusion time was in therange of from 15 to 20 min. The power consumption per batch duringextrusion was 2.4 A. A die head was employed allowing for producingcylindrical strands having a diameter of 1.7 mm. At the die head outoutlet, the strands were not subjected to a cutting to length. Thestrands thus obtained were dried for 16 h at 120° C. in a drying chamberunder air. In total (sum of the 22 batches), 97.1 kg white strands witha diameter of 1.7 mm were obtained. 65.5 kg of the dried strands weresubjected to calcination in a rotary furnace at 550° C. for 1 h underair, yielding 62.2 kg calcined strands. Thereafter, the strands weresieved (mesh size 1.5 mm), and the yield, after sieving, was 57.7 kg.The thus obtained moldings exhibited a bulk density of 322 g/l (gram perliter) and had a Zn content of 1.2 weight-%, a Ti content of 1.4weight-%, a Si content of 43 weight-%, and a C content of 0.13 weight-%.The sodium (Na) content was 0.07 weight-%.

1.8 Post-Treatment of the Molding

Starting from the calcined strands obtained according to 1.7 above, apost-treatment stage was performed as follows: 590 kg deioinized waterwere filled in a vessel. Then, 29.5 kg of the calcined moldings obtainedaccording to section 1.7 above were added. The vessel was closed(pressure-tight), and the obtained mixture was heated to a temperatureof 145° C. within 1.5 h and kept at this temperature under autogenouspressure (about 3 bar) for 8 h. Then, the mixture was cooled for 2 h.The water-treated strands were subjected to filtration and washed withdeionized water. The obtained strands were heated in a drying chamberunder air within 1 h to a temperature of 120° C. and kept at thistemperature for 16 h. Subsequently, the dried material was heated underair to a temperature of 450° C. within 5.5 h and kept at thistemperature for 2 h. Thereafter, the strands were sieved (mesh size 1.5mm), and the yield, after sieving, was 27.5 kg. The thus obtainedwater-treated moldings exhibited a bulk density of 340 g/l (gram perliter) and had a Zn content of 1.3 weight-%, a Ti content of 1.4weight-%, a Si content of 43 weight-%, and a C content of 0.10 weight-%.

Reference Example 2: Determination of Dv10, Dv50, and Dv90 Values

-   -   1. Sample Preparation: 1.0 g of the micropowder is suspended in        100 g deionized water and stirred for 1 min.    -   2. Apparatus and respective parameters used:        -   Mastersizer S long bed version 2.15, ser. No. 33544-325;            supplier: Malvern Instruments GmbH, Herrenberg, Germany        -   focal width: 300RF mm        -   beam length: 10.00 mm        -   module: MS17        -   shadowing: 16.9%        -   dispersion model: 3$$D        -   analysis model: polydisperse        -   correction: none

Reference Example 3: Determination of the Silanol Concentration

For the determination of the silanol concentration, the ²⁹Si MAS NMRexperiments were carried out at room temperature on a VARIANInfinityplus-400 spectrometer using 5.0 mm ZrO₂ rotors. The ²⁹Si MAS NMRspectra were collected at 79.5 MHz using a 1.9 microseconds pi/4 pulsewith 10 s recycle delay and 4000 scans. All ²⁹Si spectra were recordedon samples spun at 6 kHz, and chemical shifts were referenced to4,4-dimethyl-4-silapentane sulfonate sodium (DSS). For the determinationof the silanol group concentration, a given ²⁹Si MAS NMR spectrum isdeconvolved by the proper Gaussian-Lorentzian line shapes. Theconcentration of the silanol groups with respect to the total number ofSi atoms is obtained by integrating the deconvolved ²⁹Si MAS NMRspectra.

Reference Example 4: Determination of the Crush Strength of the Moldings

The crush strength as referred to in the context of the presentinvention is to be understood as determined via a crush strength testmachine Z2.5/TS1S, supplier Zwick GmbH & Co., D-89079 Ulm, Germany. Asto fundamentals of this machine and its operation, reference is made tothe respective instructions handbook “Register 1:Betriebsanleitung/Sicherheitshandbuch für die Material-PrüfmaschineZ2.5/TS1S”, version 1.5, December 2001 by Zwick GmbH & Co. TechnischeDokumentation, August-Nagel-Strasse 11, D-89079 Ulm, Germany. With saidmachine, a given strand as described in Reference Example 1 is subjectedto an increasing force via a plunger having a diameter of 3 mm until thestrand is crushed. The force at which the strand crushes is referred toas the crushing strength of the strand. The machine is equipped with afixed horizontal table on which the strand is positioned. A plungerwhich is freely movable in vertical direction actuates the strandagainst the fixed table. The apparatus was operated with a preliminaryforce of 0.5 N, a shear rate under preliminary force of 10 mm/min and asubsequent testing rate of 1.6 mm/min. The vertically movable plungerwas connected to a load cell for force pick-up and, during themeasurement, moved toward the fixed turntable on which the molding(strand) to be investigated is positioned, thus actuating the strandagainst the table. The plunger was applied to the stands perpendicularlyto their longitudinal axis. Controlling the experiment was carried outby means of a computer which registered and evaluated the results of themeasurements. The values obtained are the mean value of the measurementsfor 10 strands in each case.

Reference Example 5: ²⁹Si Solid-State NMR Spectra Regarding Q³ and Q⁴Structures

All ²⁹Si solid-state NMR experiments were performed using a BrukerAvance spectrometer with 300 MHz ¹H Larmor frequency (Bruker Biospin,Germany). Samples were packed in 7 mm ZrO₂ rotors, and measured under 5kHz Magic Angle Spinning at room temperature. ²⁹Si direct polarizationspectra were obtained using (pi/2)-pulse excitation with 5 microsecondpulse width, a ²⁹Si carrier frequency corresponding to −65 ppm in thespectrum, and a scan recycle delay of 120 s. Signal was acquired for 25ms under 45 kHz high-power proton decoupling, and accumulated over 10 to17 hours. Spectra were processed using Bruker Topspin with 30 Hzexponential line broadening, manual phasing, and manual baselinecorrection over the full spectrum width. Spectra were referenced withthe polymer Q8M8 as an external secondary standard, setting theresonance of the trimethylsilyl M group to 12.5 ppm. The spectra werethen fitted with a set of Gaussian line shapes, according to the numberof discernable resonances. Relating to the presently assessed spectra, 6lines in total were used, accounting for the five distinct peak maxima(at approximately −118, −115, −113, −110 and −104 ppm) plus a clearlyvisible shoulder at −98 ppm. Fitting was performed using DMFit (Massiotet al., Magnetic Resonance in Chemistry, 40 (2002) pp 70-76). Peaks weremanually set at the visible peak maxima or shoulder. Both peak positionand line width were then left unrestrained, i.e., fit peaks were notfixed at a certain position. The fitting outcome was numerically stable,i.e., distortions in the initial fit setup as described above did leadto similar results. The fitted peak areas were further used normalizedas done by DMFit. For the quantification of spectrum changes, a ratiowas calculated that reflects changes in the peak areas “left hand” and“right hand”, as follows. The six peaks as described were labeled with1, 2, 3, 4, 5, and 6, and the ratio Q was calculated with the formula100*{[a₁−a₂]/[a₄−a₅−a₆]}/a₃. In this formula, a_(i, i=1,6) representsthe area of the fitted peak to which this number was attributed.

Reference Example 6: Water Adsorption/Desorption

The water adsorption/desorption isotherms measurements were performed ona VTI SA instrument from TA Instruments following a step-isothermprogram. The experiment consisted of a run or a series of runs performedon a sample material that has been placed on the microbalance pan insideof the instrument. Before the measurement were started, the residualmoisture of the sample was removed by heating the sample to 100° C.(heating ramp of 5° C./min) and holding it for 6 h under a N₂ flow.After the drying program, the temperature in the cell was decreased to25° C. and kept isothermal during the measurements. The microbalance wascalibrated, and the weight of the dried sample was balanced (maximummass deviation 0.01 wt. %). Water uptake by the sample was measured asthe increase in weight over that of the dry sample. First, an adsorptioncurve was measured by increasing the relative humidity (RH) (expressedas weight-% water in the atmosphere inside of the cell) to which thesamples was exposed and measuring the water uptake by the sample atequilibrium. The RH was increased with a step of 10 wt. % from 5 to 85%and at each step the system controlled the RH and monitored the sampleweight until reaching the equilibrium conditions and recording theweight uptake. The total adsorbed water amount by the sample was takenafter the sample was exposed to the 85 weight-% RH. During thedesorption measurement the RH was decreased from 85 wt. % to 5 wt. %with a step of 10% and the change in the weight of the sample (wateruptake) was monitored and recorded.

Reference Example 7: FT-IR Measurements

The FT-IR (Fourier-Transformed-Infrared) measurements were performed ona Nicolet 6700 spectrometer. The molding was powdered and then pressedinto a self-supporting pellet without the use of any additives. Thepellet was introduced into a high vacuum (HV) cell placed into the FT-IRinstrument. Prior to the measurement the sample was pretreated in highvacuum (10⁻⁵ mbar) for 3 h at 300° C. The spectra were collected aftercooling the cell to 50° C. The spectra were recorded in the range of4000 to 800 cm⁻¹ at a resolution of 2 cm⁻¹. The obtained spectra arerepresented in a plot having on the x axis the wavenumber (cm⁻¹) and onthe y axis the absorbance (arbitrary units, a.u.). For the quantitativedetermination of the peak heights and the ratio between these peaks abaseline correction was carried out. Changes in the 3000 to 3900 cm⁻¹region were analyzed and for comparing multiple samples, a reference theband at 1880±5 cm⁻¹ was taken.

Reference Example 8: Definition and Determination of the Octanol-WaterPartition Coefficient K_(OW)

The octanol-water partition coefficient K_(OW) of a given compound isdefined as the ratio of said compound's chemical concentration in theoctanol phase relative to said compound's chemical concentration in theaqueous phase in a two-phase system of 1-octanol and water at atemperature of 25° C.

The octanol-water partition coefficient K_(OW) of a given compound isdetermined using the shake-flask method which consists of dissolving thecompound in a volume of high-purity 1-octanol and deionized water(pre-mixed and calibrated for at least 24 h) and measuring theconcentration of the compound in each the 1-octanol phase and the waterphase by a sufficiently exact method, preferably via UV/VISspectroscopy. This method is described in the OECD Guideline for thetesting of chemicals, number 107, adopted on Jul. 27, 1995.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a block diagram of a preferred process of the presentinvention. In FIG. 1, the letters and numbers have the followingmeanings:

-   -   A epoxidation unit    -   B distillation unit    -   C epoxidation unit    -   D distillation unit    -   E distillation unit    -   F distillation unit    -   G part stream distillation unit    -   H mixer-settler unit    -   I acetonitrile recovery unit    -   J acetonitrile recycle unit    -   (1)-(23) streams according to a specifically preferred process        as described in the examples    -   S0, S01, S02, S1, S2, S3, S4, S4b, S5, L1, L2, TL1, TL2, TL2,        BL2 streams according to a preferred process as described in the        general description and the examples

FIG. 2 shows a block diagram the part stream distillation G of FIG. 1unit in detail. In FIG. 1, the letters and numbers have the followingmeanings:

-   -   G1 first fractionation unit of the part stream distillation unit        G    -   G2 second fractionation unit of the part stream distillation        unit G    -   (16), (16a), (17), (18), (18a), (18b), (18c), (19), (22), (23)        -   streams according to a specifically preferred process as            described in the examples    -   S1, S2, S3, S4, S4a, S4b, S4c, S5, TL2        -   streams according to a preferred process as described in the            general description and the examples

CITED PRIOR ART

-   -   WO 2011/006990 A1    -   US 2007043226 A1    -   WO 2007/000396 A1    -   EP 0 427 062 A2    -   U.S. Pat. No. 5,194,675    -   US 2004068128 A1    -   K. J. Lissant, Making and Breaking Emulsions, Res. Lab.,        Petrolite Corp., St. Louis, Mo., USA, in: K. J. Lissant (ed.),        Emulsion Technology (1974), chapter 2, pp 111-124, Dekker, N.Y.    -   S. E. Taylor, Chem. Ind. (1992), pp 770-773

The invention claimed is:
 1. A continuous process for the preparation ofpropylene oxide, comprising (a) reacting propene, optionally admixedwith propane, with hydrogen peroxide in a reaction apparatus in thepresence of acetonitrile as solvent, obtaining a stream S0 leaving thereaction apparatus, S0 containing propylene oxide, acetonitrile, water,at least one further component B, optionally propene and optionallypropane, wherein the normal boiling point of the at least one componentB is higher than the normal boiling point of acetonitrile and whereinthe decadic logarithm of the octanol-water partition coefficient (logK_(OW)) of the at least one component B is greater than zero; (b)separating propylene oxide from S0, optionally after having separatedpropene and optionally propane, obtaining a stream S1 containingacetonitrile, water and the at least one further component B; (c)dividing S1 into two streams S2 and S3, wherein the total weight of S3relative to the total weight of S1 is in the range of from 0.01 to 25%;(d) subjecting S3 to a vapor-liquid fractionation in a firstfractionation unit, obtaining a vapor fraction stream S4a beingdepleted, relative to S3, of at least one of the at least one componentB and obtaining a liquid bottoms stream S4b, and subjecting at leastpart of the vapor fraction stream S4a to a vapor-liquid fractionation ina second fractionation unit, obtaining a vapor fraction stream S4c and aliquid bottoms stream S4 being depleted, relative to S4a, of at leastone of the at least one component B; (e) recycling at least a portion ofS4, optionally after work-up, to (a), and recycling at least a portionof S2, optionally after work-up, to (a).
 2. The process of claim 1,wherein in (c), the total weight of S3 relative to the total weight ofS1 is in the range of from 0.05 to 20%.
 3. The process of claim 1,wherein from 90 to 99.9 weight-% of S1 consist of acetonitrile and waterand wherein from 0.01 to 5 weight-% of S1 consist of the at least onecomponent B.
 4. The process of claim 1, wherein S3 is fed to the top ofthe first fractionation unit and the at least part of the vapor fractionstream S4a is fed to the bottom of the second fractionation unit,wherein in (d), the first fractionation unit is operated at an absolutepressure at the top of the first fractionation unit in the range of from0.5 to 5 bar and wherein the second fractionation unit is operated at anabsolute pressure in the bottom of the second fractionation unit in therange of from 65 to 95% of the pressure at the top of the firstfractionation unit.
 5. The process of claim 1, wherein in (d), thenumber of theoretical trays of the first fractionation unit is in therange of from 1 to 100 and the number of theoretical trays of the secondfractionation unit is in the range of from 1 to
 100. 6. The process ofclaim 1, wherein in (d), the first fractionation unit is operatedwithout reflux, the at least part of the vapor fraction stream S4asubjected to the vapor-liquid fractionation in the second fractionationunit not being condensed prior to subjecting to the vapor-liquidfractionation in the second fractionation unit, and the secondfractionation unit is operated with reflux, wherein a fraction of thevapor fraction stream S4c is used, after condensation, as reflux andwherein the reflux ratio is in the range of from 0.5:1 to 1:1.
 7. Theprocess of claim 1, wherein from 10 to 30 weight-% of the liquid bottomsstream S4b consist of acetonitrile and from 0.1 to 10 weight-% of theliquid bottoms stream S4b consist of the at least one further componentB.
 8. The process of claim 1, wherein from 90 to 99.99 weight-% of S4consist of acetonitrile and water, and wherein from 0.0001 to 0.2weight-% of S4 consist of the at least one component B.
 9. The processof claim 1, wherein (e) comprises working-up S4, said working-upcomprising combining at least a portion of S4 with S2 obtaining a liquidstream.
 10. The process of claim 9, wherein (e) comprises subjecting theliquid stream to acetonitrile-water separation obtaining a streamenriched in acetonitrile, and recycling said stream enriched inacetonitrile, optionally after further work-up, to (a).
 11. The processof claim 10, wherein (e) comprises (i) preparing a liquid stream S5 byadding a liquid stream P to S2, or to at least the portion of S4, or tothe liquid stream obtained from combining S2 and at least the portion ofS4, wherein P comprises at least 95 weight-% of C3, based on the totalweight of P, wherein C3 is propene optionally admixed with propane witha minimum weight ratio of propene relative to propane of 7:3, andwherein P is added in an amount so that in S5, the weight ratio of C3relative to acetonitrile is in the range of from 0.2:1 to 5:1; (ii)subjecting S5 to a temperature of 92° C. at most and a pressure of atleast 10 bar, obtaining a first liquid phase L1 and a second liquidphase L2, wherein at least 95 weight-% of L1 consist of C3,acetonitrile, water and the at least one component B, the water contentof L1 being less than 10 weight % based on the total weight of L1, andwherein at least 95 weight-% of L2 consist of C3, acetonitrile, waterand the at least one component B, the C3 content of L2 being 5 weight-%at most, based on the total weight of L2, and the acetonitrile contentof L2 being less than 45 weight-% based on the total weight of L2; (iii)separating L1 from L2; (iv) recycling L1 as the stream enriched inacetonitrile, optionally after further work-up, to (a).
 12. The processof claim 11, further comprising working up L1, said working-upcomprising subjecting L1 to a distillation stage wherefrom a bottomsstream BL1 is obtained, wherein at least 95 weight-% of BL1 consist ofC3, acetonitrile, water and the at least one component B, wherein the C3content of BL1 is in the range of from 7 to 18 weight-%, and recyclingBL1 as the stream enriched in acetonitrile, optionally without anyfurther work-up, to (a).
 13. The process of claim 12, wherein from 0.01to 5 weight-%, of BL1 consist of the at least one component B.
 14. Theprocess of claim 1, wherein (b) comprises (I) separating propene,optionally together with propane, and oxygen which is optionallyadditionally contained in S0, from S0, obtaining a stream S01 enrichedin propylene oxide, acetonitrile, water, and the at least one componentB, wherein at least 99 weight-% of S01 consist of acetonitrile, water,the at least one component B and propylene oxide; wherein forseparation, a fractionation unit is used, wherein at the top of thefractionation unit, liquid acetonitrile, optionally admixed with liquidwater, is added as entraining agent; (II) separating propylene oxidefrom S01, obtaining a stream S02 enriched in acetonitrile, water and theat least one component B, wherein at least 95 weight-% of S02 consist ofacetonitrile, water and the at least one component B, and wherein theweight ratio of acetonitrile relative to water is greater than 1:1,wherein S02 is subjected to (c) as S1.
 15. The process of claim 14,wherein (b) further comprises (IIIa) subjecting S02 obtained from (II)to hydrogenation; and/or (IIIb) subjecting the stream obtained from (II)or (IIIa) to distillation to obtain a bottoms stream, wherein thehydrogenated stream obtained from (IIIa) or the bottoms stream obtainedfrom (IIIb) is subjected to (c) as S1.
 16. The process of claim 1,wherein in (a), propene is reacted with hydrogen peroxide in thepresence of a heterogeneous catalyst, said heterogeneous catalystcomprising a zeolite.
 17. The process of claim 1, wherein from 90 to 97weight-% of S0 consist of acetonitrile, water, and propylene oxide, andwherein from 0.01 to 3 weight-% of S0 consist of the at least onecomponent B.
 18. The process of claim 1, wherein the at least onecomponent B is propionitrile, 1-nitropropane, 2-nitropropane,3-methylbutanenitrile, n-pentanenitrile, 1-pentanol, 2-pentanol,2-butanone, 2-pentanone, 2-hexanone, 4-methyl-2-heptanone,2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, 4,6-dimethyl-2-heptanone,2,6-dimethyl-4,6-heptandiol, 2,4-dimethyloxazoline,2,5-dimethyloxazoline, cis-2,4-dimethyl-1,3-dioxolane,trans-2,4-dimethyl-1,3-dioxolane, acetaldehyde, propionaldehyde, atleast one impurity contained in the hydrogen peroxide employed in (a),or a combination of two or more of these compounds.
 19. The process ofclaim 18, wherein the at least one component B comprises a combinationof propionitrile, 1-nitropropane, 2-nitropropane,2,6-dimethyl-4-heptanol, 4,6-dimethyl-2-heptanol,2,6-dimethyl-4-heptanone, acetaldehyde, and propionaldehyde.
 20. Theprocess of claim 18, wherein in (d), the stream S3 is subjected to avapor-liquid fractionation in a first fractionation unit, obtaining avapor fraction stream S4a being depleted, relative to S3, of at leastone of the at least one component B, the at least one of the at leastone component B comprising propionitrile, or 1-nitropropane, or2-nitropropane, or 2,6-dimethyl-4-heptanol, or 4,6-dimethyl-2-heptanol,or 2,6-dimethyl-4-hepta-none, or a combination of two or more thereof,and obtaining a liquid bottoms stream S4b, wherein at least part of thevapor fraction stream S4a is subjected to a vapor-liquid fractionationin a second fractionation unit, obtaining a vapor fraction stream S4cand a liquid bottoms stream S4 being depleted, relative to S4a, of atleast one of the at least one component B, the at least one of the atleast one component B comprising acetaldehyde, or propionaldehyde, or2-butanone, or a combination of two or more thereof.
 21. The process ofclaim 18, wherein the at least one impurity contained in the hydrogenperoxide employed in (a) is selected from the group of compoundsconsisting of an alkyl phosphate, a nonyl alcohol, an alkylcyclohexanolester, an N,N-dialkyl carbonamide, an N-alkyl-N-aryl carbonamide, anN,N-dialkyl carbamate, a tetraalkyl urea, a cycloalkyl urea, aphenylalkyl urea, an N-alkyl-2-pyrrolidone, an N-alkyl caprolactam, anda combination of two or more of these compounds.
 22. The process ofclaim 1, wherein in (d), 90 to 100 weight-% of the vapor fraction streamS4a are subjected to the vapor-liquid fractionation in the secondfractionation unit.